$ Seive tubes in plants are formed of enucleated cells called seive members.
! All the activities of a seive cell are controlled by nucleated parenchyma cells.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

### Step-by-Step Solution:

1. **Understanding Sieve Tubes**:
- Sieve tubes are specialized structures in plants responsible for the transport of nutrients, particularly sugars. They are composed of enucleated cells known as sieve members.

2. **Assertion Analysis**:
- The assertion states that "sieve tubes in plants are formed of enucleated cells called sieve members." This is correct because sieve members lack a nucleus and are indeed the building blocks of sieve tubes.

3. **Reason Analysis**:
- The reason provided is that "all the activities of a sieve cell are controlled by nucleated parenchyma cells." This statement is incorrect. While parenchyma cells are involved in various functions in plants, the activities of sieve cells are specifically regulated by companion cells, which are specialized parenchyma cells that are closely associated with sieve tubes.

4. **Conclusion**:
- Therefore, the assertion is correct, but the reason is incorrect. The correct relationship is that companion cells, not general parenchyma cells, control the activities of sieve cells.

### Final Answer:
- Assertion: Correct
- Reason: Incorrect

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