Q. no 19 is Assertion - Reasoning based questions.
These consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
Assertion (A): Capillaries have walls that are just one cell thick.
Reason (R): Exchange of material between the blood and surrounding cells takes place across the capillaries.

Options

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