The distance between Earth and Sun is called the astronomical unit and its value is about 93 million miles. This has been known since ancient times...

The distance between Earth and Sun is called the astronomical unit and its value is about 93 million miles. 

A. This has been known since ancient times by studying eclipses

B. Was determined by Galileo with his telescope in 1609

C. Has been measured during transits of Venus during the past 200 years

D. The value was unknown until space travel became a reality in the twentieth century