The fact, that `C_(3)` plants respond to higher `CO_(2)` concentration and show higher productivity, has been used for some greenhouse crops such as :-

Options

A. Maize & Tomatoes
B. Bell pepper & Sorghum
C. Maize & Sorghum
D. bell pepper & Tomatoes

Answer

To solve the question regarding which greenhouse crops respond to higher CO2 concentrations and are considered C3 plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding C3 Plants**:
- C3 plants utilize the Calvin cycle for photosynthesis, where carbon dioxide (CO2) is fixed into a three-carbon compound. They are known to respond positively to increased CO2 levels, leading to higher productivity.

2. **Identifying Greenhouse Conditions**:
- Greenhouse crops typically require controlled conditions, including higher CO2 concentrations and elevated temperatures, to maximize growth and yield.

3. **Evaluating the Options**:
- We need to analyze the provided options to identify which pairs of plants are known to thrive in greenhouse conditions.

4. **Analyzing Each Pair**:
- **Option 1: Maize and Tomato**:
- Maize is primarily a C4 plant and prefers rainy conditions, while tomato is a C3 plant that thrives in warm conditions.
- **Option 2: Bell Pepper and Sorghum**:
- Bell pepper is a C3 plant that grows well in warm conditions, but sorghum is typically a C4 plant suited for drier climates.
- **Option 3: Maize and Sorghum**:
- Both are C4 plants and not suitable for greenhouse conditions.
- **Option 4: Bell Pepper and Tomato**:
- Both are C3 plants that thrive in higher temperatures and respond well to increased CO2 levels, making them suitable greenhouse crops.

5. **Selecting the Correct Answer**:
- Based on the analysis, the correct option is **Bell Pepper and Tomato** as both are C3 plants that benefit from higher CO2 concentrations in greenhouse environments.

### Final Answer:
The correct answer is **Bell Pepper and Tomato**.

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