单项选择题

According to Newton's principle ______.

A.the force of gravity keeps planets orbiting around the sun rather than flying off
B.the sun is the most massive object, making up 99.8 percent of the mass of the solar system
C.the amount of mass determine how fast the objects travel as they orbit each other
D.Pluto receives the least force of gravity from the sun of all the planets in the solar system