USMLE Step 1 practice questions: the prompt for ChatGPT, Claude and Gemini

You are writing exam-style multiple-choice practice questions for me. I am preparing for USMLE Step 1, set by FSMB and NBME. Write questions that match the real exam's content, difficulty and style, drawn from the current official syllabus.

Write 20 questions. Each must be a standalone multiple-choice question that can be answered from its own stem and options, with exactly the right answer(s) marked and nothing ambiguous.

Set each question's `topic` to one of these names, copied exactly (same words, same capitalization; these are the only topic names the import accepts):
- Human Development (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Blood & Lymphoreticular/Immune Systems (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Behavioral Health & Nervous Systems/Special Senses (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Musculoskeletal, Skin & Subcutaneous Tissue (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Cardiovascular System (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Respiratory & Renal/Urinary Systems (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Gastrointestinal System (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Reproductive & Endocrine Systems (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Multisystem Processes & Disorders (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Biostatistics & Epidemiology/Population Health (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
- Social Sciences: Communication and Interpersonal Skills (subtopics: Pathology; Physiology; Nutrition; Gross Anatomy & Embryology; Microbiology; Pharmacology; Behavioral Sciences; Biochemistry; Histology & Cell Biology; Immunology; Genetics)
Where subtopics are listed, set `subtopic` to one of them; otherwise choose a short, specific `subtopic` of your own or leave it out.

Spread the questions across the topics in the real exam's proportions, about:
- Human Development: 0 (1–3% of the real exam)
- Blood & Lymphoreticular/Immune Systems: 2 (9–13% of the real exam)
- Behavioral Health & Nervous Systems/Special Senses: 2 (10–14% of the real exam)
- Musculoskeletal, Skin & Subcutaneous Tissue: 2 (8–12% of the real exam)
- Cardiovascular System: 2 (7–11% of the real exam)
- Respiratory & Renal/Urinary Systems: 3 (11–15% of the real exam)
- Gastrointestinal System: 2 (6–10% of the real exam)
- Reproductive & Endocrine Systems: 3 (12–16% of the real exam)
- Multisystem Processes & Disorders: 2 (8–12% of the real exam)
- Biostatistics & Epidemiology/Population Health: 1 (4–6% of the real exam)
- Social Sciences: Communication and Interpersonal Skills: 1 (6–9% of the real exam)

Give each question between 4 and 6 options. Options are plain text without letter prefixes (DoMcq labels them A, B, C… by position); make them similar in length and form so the right one does not stand out.
Every question has exactly one correct option; `answer` is a single letter.
Never use these as an option: "all of the above", "none of the above". Avoid "both A and B" style options too.

Write stems the way the real exam does, for example: "Which of the following is the most likely diagnosis?"; "Which of the following is the most likely underlying cause of this patient's condition?"; "Which of the following is the most appropriate initial response by the physician?"; "Which of the following infectious agents is the most likely cause of these findings?".
Keep each stem self-contained (any scenario the question needs is in the stem), concrete and free of trick wording. Do not refer to other questions, images, tables or exhibits.
Every item is a standard multiple-choice question: do not write image-based, audio, long-list (7 or more options) items.

Mix the difficulty: about 6 easy, 10 medium and 4 hard, and set each question's `difficulty` to "easy", "medium" or "hard" accordingly.

In `explanation`, say in two to four sentences why the correct answer is correct, in a way that teaches the underlying point, not just restates the option.

In `source`, give a short reference I can check in my own study materials (a syllabus topic, a chapter or section name, a learning objective, or a standard's clause), at most 200 characters; never invent a page number or a quotation.

Leave out `rationales` and `id`.

Before you answer, check your own work: no two questions ask the same thing; no question gives away another's answer; the correct option sits in a different position from one question to the next (never always the same letter); every `answer` letter exists for that question; the correct option is correct according to the current official material, not folklore; facts are accurate. Fix anything you find.

Output the whole set as one JSON object in the `domcq/1` format (schema: https://domcq.com/schema/v1; this is the import format of https://domcq.com):

```json
{
  "format": "domcq/1",
  "exam": "usmle-step1",
  "set": "USMLE Step 1 practice – [a short name for this set]",
  "questions": [
    {
      "stem": "[the question, 10–2000 characters]",
      "options": [
        "[option 1]",
        "[option 2]",
        "[option 3]",
        "[option 4]"
      ],
      "answer": "B",
      "explanation": "[why the correct answer is correct, 1–3000 characters]",
      "topic": "Human Development",
      "subtopic": "[optional, more specific]",
      "difficulty": "medium",
      "source": "[a reference I can check]"
    }
  ]
}
```

Rules the import enforces: `format` is exactly "domcq/1"; `set` is 1–120 characters; `questions` holds all 20; each question has exactly the fields shown (no others); `stem` is 10–2000 characters and each option 1–500; `options` are all different; `answer` uses capital letters A–F naming options by position, in ascending order, never every option; `explanation` (1–3000 characters) and `topic` are required; `subtopic` (up to 120 characters), `difficulty` ("easy", "medium" or "hard") and `source` (up to 200 characters) are optional. Use plain double quotes in JSON strings (escape any inside text as \"), no trailing commas, no comments.

Reply with the JSON object inside a single ```json code fence and nothing else: no introduction, no commentary, no notes after it. If the set is long, keep going until every question is written and the JSON is complete and closed.