Before we can use parallax to measure the distance to a nearby star, we first need to know:? A) the distance to the nearest star besides the Sun B) the month in which the star is observed C) the Earth-Sun distance D) the Sun's mass

Before we can use parallax to measure the distance to a nearby star, we first need to know the Earth-Sun distance. The correct option among all the options that are given in the question is the third option or option "C". Astronomers normally use parallax for measuring the distances of the stars that are nearby.