Herbicide resistant gene is

Options

A. Ct
B. Mt
C. Bt
D. GST

Explanation

### Step-by-Step Solution:

1. **Understanding Herbicide Resistance**:
- Herbicide resistance refers to the ability of plants to survive and thrive despite the application of herbicides, which are chemicals designed to kill unwanted plants (weeds) that compete with crops for resources.

2. **Identifying the Gene**:
- The question asks for the specific gene that confers herbicide resistance. We have four options to consider: CT, MT, Bt, and Gst.

3. **Examining the Options**:
- **CT**: Not commonly associated with herbicide resistance.
- **MT**: Also not recognized as a herbicide-resistant gene.
- **Bt**: This gene is known for providing resistance against certain pests (insect resistance), not herbicides.
- **Gst**: This stands for Glutathione S-Transferase, which is known to confer herbicide resistance.

4. **Source of the Gst Gene**:
- The Gst gene is isolated from a bacterium known as *Steptomyces hydrolyticus*. This gene allows transgenic plants to withstand herbicide applications, thus protecting the crops while eliminating weeds.

5. **Conclusion**:
- Based on the information provided, the correct answer to the question is the Gst gene, which is option number 4.

### Final Answer:
The herbicide resistant gene is the Gst gene (Glutathione S-Transferase gene).

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