Assertion (A) A man standing on a completely frictionless surface can bring himself in motion by whistling. Reason (R) If there is no external force acting on a system, then its momentum cannot change.

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R and R is not the correct explanation of A.
• C. A is right but R is wrong
• D. A is wrong but R is right