Answer:
A. a crest that is toppling over.
Step-by-step explanation:
As we know that at the position of crest in a wave the velocity of motion of molecules is the least velocity or zero velocity
So as the surfer needs the stability he need a point of least velocity and maximum stability
So in that case he has to travel at the position of crest where he can obtain maximum stability and then his speed will be same as the speed of wave propagation in the direction of wave
so here correct answer would be
A. a crest that is toppling over.