A Vehicle Has Power Assist During Engine Operation, but It

A vehicle has power assist during engine operation, but it has no assist after the engine has been off and during initial engine startup. Technician A says a stuck close vacuum check valve could be the cause. Technician B says a leaking vacuum check valve could be the cause. Who is correct?

A) A only
B) B only
C) Both A and B
D) Neither A nor B