Why Do We Say That the Doppler Technique Gives the Planet's

Multiple Choice

Why do we say that the Doppler technique gives the planet's "minimum mass"?

A) The size of the Doppler shift that we detect depends on whether the planet's orbit is tilted.
B) The size of the Doppler shift that we detect depends on knowing the star's mass,which can be very uncertain.
C) Extrasolar planets are always increasing in mass.
D) Doppler measurements are very difficult,producing noisy data that often cause astronomers to underestimate a planet's mass.