Which of the following statements about stellar parallax is true?
a. we observe all stars to exhibit at least a slight amount of parallax.
b. stellar parallax was first observed by ancient greek astronomers.
c. the amount of parallax we see depends on how fast a star is moving relative to us.
d. the closer a star is to us, the more parallax it exhibits.
e. it takes at least 10 years of observation to measure a star's parallax.

c. The amount of parallax we see depends on how fast a star is moving relative to us.

Explanation:

The stellar parallax is obtained by  a mathematical calculation, is a geometrical measure among the Earth and another star. For example, by now, it is known the distance from the Earth to the sun, so, is like this star can be observed by two eyes. The Earth and the Sun. If we joined the two lines from the Earth and the Sun too the star, it will form a triangle. With some calculation and the angle formed, it can be determined the distance to the star.

Hope it was useful.