Why Does the Doppler Shift Method of Detecting Extrasolar Planets

Why does the Doppler shift method of detecting extrasolar planets only give us the minimum mass of a planet?

A) because we don't necessarily know the density of the planet
B) because we don't necessarily know the angle the planet's orbit makes with our line of sight
C) because we don't necessarily know the diameter (size) of the planet
D) because we don't necessarily know the mass of the parent star very