As Astronomers Use the Term, the Parallax of a Star

As astronomers use the term, the parallax of a star is

A) one half of the Doppler shift due to its radial velocity
B) always equal to 1 AU
C) one half the angle that a star shifts when seen from opposite sides of the Earth's orbit
D) the time it takes a Cepheid variable star to go through one cycle of its brightness changes
E) the time it takes for a star to move one second of arc of proper motion