You See a System Consisting of a Mass Oscillating on the End

You see a system consisting of a mass oscillating on the end of a spring passed you at a speed u and note that the period of the system is T.Your strange friend,who is moving with the mass-spring system,also measures its period and finds a period that is

A) equal to T.
B) less than T.
C) greater than T.
D) either a or b depending on whether the system was approaching or receding from the first observer.
E) There is not sufficient information to answer the question.