Assertion :- The members of phylum Aschelminthes are called round worms.
Reason :- The body of the Aschelminthes is circular in cross-section .

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
- The assertion states: "The members of phylum Aschelminthes are called round worms."
- This statement is **true**. Members of the phylum Aschelminthes, which includes organisms like nematodes, are indeed referred to as roundworms.

### Step 2: Analyze the Reason
- The reason states: "The body of the Aschelminthes is circular in cross-section."
- This statement is also **true**. The body structure of Aschelminthes is indeed circular in cross-section, which is a characteristic feature of roundworms.

### Step 3: Determine the Relationship
- Now we need to determine if the reason correctly explains the assertion. Since the assertion is about the classification of Aschelminthes as roundworms, and the reason provides a characteristic (circular cross-section) that defines them, we can conclude that the reason is indeed a correct explanation of the assertion.

### Conclusion
- Since both the assertion and the reason are true, and the reason correctly explains the assertion, the correct answer is:
**Option 1: Both assertion and reason are true, and reason is the correct explanation of assertion.**