[单选题]
The Michelson-Morley expel uuh -t,bps,-riment was designed to mow6l xj:,2m.iq.nq7ox/ hyy kexb. u) easure
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.