`CO_(2)` combines with RuBP in the presence of enzyme RuBisCO to from 3PGA This process of Calvin cycle is included under

Options

A. (a) carboxylation
B. (b) oxygenation
C. (c) reduction
D. (d) regeneration

Explanation

To solve the question about the process in which carbon dioxide combines with RuBP in the presence of the enzyme RuBisCO to form 3-phosphoglyceric acid (3PGA) during the Calvin cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components**:
- Recognize that RuBP stands for ribulose bisphosphate and is the starting substrate in the Calvin cycle.
- Understand that the enzyme involved in this reaction is RuBisCO.

2. **Understand the Reaction**:
- The reaction in question involves carbon dioxide (CO₂) combining with RuBP to form 3-phosphoglyceric acid (3PGA).
- This reaction is a crucial step in the Calvin cycle.

3. **Determine the Phase of the Calvin Cycle**:
- The Calvin cycle consists of three main phases:
- Carboxylation
- Reduction
- Regeneration
- The specific step where CO₂ combines with RuBP is known as carboxylation.

4. **Conclusion**:
- Since the question specifically asks about the process where CO₂ combines with RuBP to form 3PGA, the answer is that this process is included under **Carboxylation**.

5. **Final Answer**:
- Therefore, the correct answer is **Option A: Carboxylation**.