Name the lymphoid organ in humans where all the blood cells are produced.

Explanation

**Step-by-Step Solution:**

1. **Identify the Type of Organ**: Understand that the question is asking for a lymphoid organ in humans responsible for the production of blood cells.

2. **Differentiate Between Lymphoid Organs**: Recognize that there are two types of lymphoid organs: primary and secondary lymphoid organs.

3. **Focus on Primary Lymphoid Organs**: Since the question specifically asks where blood cells are produced, focus on primary lymphoid organs, as these are responsible for the production of blood cells.

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