Bt-cotton is resistant to:

Options

A. insects
B. herbicides
C. salt
D. drought

Answer

### Step-by-Step Solution:

1. **Understanding Bt-Cotton**: Bt-cotton is a genetically modified organism (GMO) that has been engineered to express a specific protein that provides resistance to certain pests.

2. **Source of Bt Toxin**: The Bt toxin used in Bt-cotton is derived from the bacterium *Bacillus thuringiensis*. This bacterium produces a protein that is toxic to certain insects.

3. **Mechanism of Resistance**: The gene coding for the Bt toxin is inserted into the cotton plant's genome. When insects feed on the cotton, they ingest the Bt toxin.

4. **Activation of Bt Toxin**: Once ingested, the Bt toxin is activated in the alkaline environment of the insect's gut. It changes from an inactive form (protoxin) to an active form.

5. **Effect on Insects**: The activated Bt toxin binds to specific receptors in the midgut of the insect, leading to the disruption of gut cells and ultimately causing the death of the insect.

6. **Conclusion**: Therefore, Bt-cotton is resistant to insect pests, specifically those that are susceptible to the Bt toxin. It does not provide resistance to herbicides, salt, or drought conditions.

### Final Answer:
Bt-cotton is resistant to insect pests due to the presence of the Bt toxin derived from *Bacillus thuringiensis*.

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