Which is correct?

Options

A. (a) `C_(4)` plants are more efficient than `C_(3)` plants
B. (b) `C_(3)` plants are more efficient than `C_(4)` plants
C. (c) Photorespiration is useful process
D. (d) Photorespiration is about in `C_(3)` plants

Answer

To determine which statement is correct regarding photosynthesis and the efficiency of C3 and C4 plants, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Analyze Option A: "C4 plants are more efficient than C3 plants."**
- This statement is **correct**. C4 plants have a unique mechanism that allows them to minimize photorespiration, a process that can waste energy and reduce efficiency in C3 plants. C4 plants are adapted to high light intensity and temperature, which enhances their photosynthetic efficiency.

2. **Analyze Option B: "C3 plants are more efficient than C4 plants."**
- This statement is **incorrect**. As mentioned in Option A, C4 plants are more efficient due to their ability to avoid photorespiration, which is prevalent in C3 plants.

3. **Analyze Option C: "Photorespiration is a useful process."**
- This statement is **incorrect**. Photorespiration is generally considered a wasteful process because it consumes energy (ATP) and does not contribute to the production of glucose, which is the primary goal of photosynthesis.

4. **Analyze Option D: "Photorespiration occurs in C3 plants."**
- This statement is somewhat misleading. While it is true that photorespiration occurs in C3 plants, the statement implies that photorespiration is exclusive to C3 plants. Photorespiration is associated with the enzyme Rubisco, which is present in both C3 and C4 plants, but it is more pronounced in C3 plants. Therefore, this statement is **incorrect** as it does not fully capture the context.

### Conclusion:
The correct statement is **Option A: C4 plants are more efficient than C3 plants.**