Assertion (A): All chordates possess open circulatory system.
Reason (R): Balanoglossus possesses open blood vascular system.

Options

A. Both A and R are true and R is the correct explanation for A.
B. Both A and R are true but R is not the correct explanation for A.
C. A is true and R is false.
D. A is false and R is true.

Explanation

To analyze the assertion and reason provided in the question, we can break down the statements step by step:

### Step 1: Understand the Assertion
- **Assertion (A)** states that "All chordates possess an open circulatory system."
- This statement is **incorrect** because chordates, which include animals such as mammals, birds, reptiles, amphibians, and fish, generally possess a **closed circulatory system**. In a closed circulatory system, blood is contained within blood vessels.

### Step 2: Understand the Reason
- **Reason (R)** states that "Balanoglossus possesses an open blood vascular system."
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