What Is the Baseline That Astronomers Use to Measure the Parallax

Multiple Choice

What is the baseline that astronomers use to measure the parallax (the distance) of the nearest stars?

A) the diameter of the Earth
B) the distance between observatories in Greenwich, England and Washington, DC
C) the distance between the Earth and the Moon
D) ½ the diameter of the Earth's orbit around the Sun
E) no one can measure parallax for the stars; only for planets in our solar system