The Radial Velocity Curve of a Star in a Binary

Multiple Choice

The radial velocity curve of a star in a binary star system is a plot against time of the:

A) speed of the star in a direction perpendicular to the line of sight to the star.
B) position of the star in celestial coordinates.
C) variation of Doppler shift of the star's spectral lines and hence of its speed toward or away from us.
D) temperature of the star as determined from the movement of the peak wavelength of its spectrum.