In the following questions $19 \& 20$, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct answer out of the following choices : (A) Both (A) and (R) are true and (R) is the correct explanation of (A). (B) Both (A) and $( R )$ are true, but $( R )$ is not the correct explanation of (A). (C) (A) is true, but (R) is false. (D) (A) is false, but (R) is true.