`C_(4)` cycle was discovered by

Options

A. Hatch and Slack
B. Calvin
C. Hill
D. Arnon

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks who discovered the C4 cycle, which is a crucial process in photosynthesis that occurs in certain plants.

2. **Identifying the Options**: The options provided are:
- A. Hatch and Slack
- B. Calvin
- C. Hill
- D. Amel

3. **Analyzing Each Option**:
- **Option A (Hatch and Slack)**: These two scientists are known for their research on the C4 cycle. They discovered this pathway that allows certain plants to efficiently fix carbon dioxide.
- **Option B (Calvin)**: Melvin Calvin is known for discovering the C3 cycle, not the C4 cycle.
- **Option C (Hill)**: Hill is recognized for his work related to the role of oxygen in photosynthesis, not specifically for the C4 cycle.
- **Option D (Amel)**: Amel is known for contributions related to light in photosynthesis, but not for the C4 cycle.

4. **Conclusion**: Based on the analysis, the correct answer is **A. Hatch and Slack**, as they are the scientists credited with the discovery of the C4 cycle.

**Final Answer**: The C4 cycle was discovered by **Hatch and Slack**.

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