Assertion (A): A man standing on a completely frictionless surface can propel himself by whistling.
Reason (R): If no external force acts on a system, its momentum cannot change.

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

Answer: Option B