A sensitive thread-like structure which can coil around a support is

Options

A. Spring
B. Tendril
C. Rachis
D. Twiner.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a sensitive, thread-like structure that can coil around a support. We need to identify which of the given options fits this description.

2. **Analyzing the Options**:
- **Spring**: This is typically a coiled metal device used for tension or compression. It does not fit the description of a sensitive, thread-like structure.
- **Tendril**: This is a slender, thread-like structure found in climbing plants. Tendrils are sensitive and can coil around supports to help the plant climb.
- **Rachis**: This term refers to the main axis of a compound leaf, not a structure that coils around supports.
- **Twinner**: This refers to a type of climbing plant but does not specifically describe a structure that coils.

3. **Identifying the Correct Answer**: Among the options, the only structure that is sensitive, thread-like, and capable of coiling around a support is the **tendril**.

4. **Conclusion**: Therefore, the correct answer to the question is **tendril**.

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