Explain the earth's motion through space, including precession, nutation, the barycenter, and its path about the galaxy.

Precision refers to the change in the direction of the axis, however, it does not lead to any change in the tilt. It changes the stars near the pole, however, does not affect the seasons.  

Nutation refers to wobbling around the precessional axis, that is, half a degree one way or the other. It has a period of 18 years and takes place because of the Moon, it slightly influences seasons.  

Barycenter refers to the point in between the two objects where they counteract each other. The Moon does not orbit around the definite center of the Earth, however, at around a point where the two masses balance each other out.  

The galaxy refers to a huge group of star clusters, dust, single stars, a system of stars, and gas bound together by gravity.  

hey there!

mass = 6.75 g

volume =   9 cm³

therefore:

d = mass / volume

d   = 6.75 / 9

d = 0.7 g/cm³

answer b