[单选题]
The Michelson-Morley experi yx;jd ;4 n; y(c*iyorbo4mq9qn y01p-fqre;nment 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.