The structure of DNA was proposed by

Options

A. Schleiden and Schwann
B. Watson and Crick
C. Darwin and Wallace
D. Mendel and Morgan

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks who proposed the structure of DNA. This is a historical inquiry into the discovery of DNA's structure.

2. **Identifying the Options**: The options provided are:
- Schleiden and Schwann
- Watson and Crick
- Darwin and Wallace
- Mendel and Morgan

3. **Analyzing Each Option**:
- **Schleiden and Schwann**: They are known for cell theory, not DNA structure.
- **Watson and Crick**: They are credited with proposing the double helix structure of DNA.
- **Darwin and Wallace**: They are known for their work on evolution and natural selection.
- **Mendel and Morgan**: Mendel is famous for his work on inheritance, while Morgan worked on genetics with fruit flies.

4. **Conclusion**: After analyzing the options, it is clear that Watson and Crick are the scientists who proposed the structure of DNA. They described it as a double helix, which is a significant contribution to biology.

5. **Final Answer**: The structure of DNA was proposed by **Watson and Crick**.

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