The correct answer is D He could pull the mass down farther.
Amplitude, is the maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. So to increase the amplitude the spring should be pulled down further which can increase the amplitude.
The difference between speed and velocity is that the speed is a scalar quantity which means that you can say that this object has a speed of x m/s but you don't have to define its direction
while the velocity is a vector quantity which means that you have to express the velocity by which it moves in x,y and z directions and its norm is the speed
