[单选题]
The Michelson-Morleyvt4bjhc ; mxf /+5cvnrw s5 /b: 1dk;1+cmfxfa experime14pfy 7) 1cxjd4qcko6yqu mmpb*jn91 nt 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.