Assertion (A): When a wire is stretched to three times its length, its resistance becomes 9 times.
Reason (R): Resistance is directly proportional to the length of the wire.

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.