[单选题]
The Michelson-Morley experiment was desiu)/8m:k nj ox/xco+dqgned to mea n:p/avrj )b bs30q;f6pay ew5sure
A. the relativistic mass of the electron.
B. the relativistic energy of the electron.
C. the velocity of the Earth relative to the ether.
D. the acceleration of gravity on the Earth's surface.
