Jupiter's Mass Is More Than 300 Times the Mass of Earth

Jupiter's mass is more than 300 times the mass of Earth, and Saturn has almost 100 times Earth's mass. These masses were determined by:

A) watching carefully the orbits of these planets around the Sun.
B) measuring the deviations of the other planets from their expected orbits around the Sun.
C) measuring the deflection of Halley's comet from its orbit when it is near Jupiter and Saturn.
D) measuring the orbits of the satellites of these planets.