Not a perfect ball
Earth is shaped like a sphere, but rotation makes it bulge at the equator and flatten a little at the poles. Picture a slightly squashed ball. That shape is called an oblate spheroid — on the test, sphere and poles are the words they want.
Gravity is a force
Gravity is a force that every object exerts on all other objects. You pull on Earth and Earth pulls on you. Earth's pull is just much stronger because Earth has far more mass.
Density turns up the pull
Density is the amount of mass per volume. Pack more mass into the same space and the gravitational pull gets greater. That is why the dense iron core pulls so strongly, and why fill-in #4 is “object” and “greater.”