In 1959, Pound and Rebka Did an Experiment to Test

In 1959, Pound and Rebka did an experiment to test the prediction of Einstein's theory of general relativity about the relationship between the pace of time and the strength of gravity. When two identical atomic clocks, one on the ground floor and one on the top floor, were compared,

A) the clocks ran at exactly the same pace in both locations
B) the clock on the top floor ran a tiny bit slower
C) the clock on the ground floor ran a tiny bit slower
D) the clock on the ground floor became a little bit lighter (weighed less)
E) the clock on the top floor became a little bit lighter