Read the excerpt from A Black Hole is NOT a Hole.

According to Newton, the force of gravity is a two-way tug between any two objects. It works with anything—any matter at all. The matter can be a tiny bit of a thing, as small as a speck of stardust. It can be a huge collection of material, as gigantic as a galaxy. It can be as rigid as rock or as flimsy as flame. No matter what it is, if it's made of matter, then it possesses the power to pull on anything else.

According to context clues, which is the best definition of gravity?

A.)a dropping object
B.)a pull between objects
C.)a collection of material
D.)a rigid rock