One of the First Tests of the General Theory of Relativity

One of the first tests of the general theory of relativity was the ____.

A) description of the orbit of the Moon
B) determination of the speed of light as a constant
C) change in mass of a particle moving at a high speed
D) demonstration of a hammer and a feather falling at the same rate on the Moon
E) determination of the rate of advance of the perihelion of Mercury's orbit