What Was the First Evidence That Gravity Outside Our Solar

Multiple Choice

What was the first evidence that gravity outside our solar system worked the same way as it does inside?

A) Galileo saw through his early telescope that the Milky Way consisted of many stars
B) Herschel measured the two stars that make up the Castor system moved around each other
C) Cannon measured different lines in the spectra of different types of stars
D) Comet Halley returned after a 76-year absence
E) You can't fool me, we still don't know whether gravity around other stars works the same way as it does here