[单选题]
The Michelson-Morley experimx.o 2hy67 lep-//s)*lcvldlbi,4 tfv)hs b (fs ov6ument was designed to measure
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.