A mass m attached to a spring of constant k is oscillating on a frictionless surface. A second mass of mass m is dropped on top of the first at the moment the spring is extended to the end (x = A). Which of the following is true?
A. The maximum velocity does not change.
B. The amplitude of the oscillation A decreases.
C. The frequency of oscillations f does not change.
D. The frequency of oscillations f increases.
E. The period of oscillation increases.