Observer a Sees a Pendulum Oscillating Back and Forth in a Relativistic

Multiple Choice

Observer A sees a pendulum oscillating back and forth in a relativistic train and measures its period to be T_A. Observer B moves together with the train and measures the period of the pendulum to be T_B. These two results will be such that

A) T_A > T_B.
B) T_A = T_B.
C) T_A < T_B.
D) T_A could be greater or smaller than T_B depending on the direction of the motion.