From where on earth could you observe all of the stars during the course of a year? what fraction of the sky can be seen from the north pole?

The equator

Half

Explanation:

From the equator a person can observe all of the stars during the course of a year. This is because the equator is the part of the Earth where the upward and downward curve of the sphere of Earth meet.

When you are at the North pole you will only be able to see what is visible from the North pole and the southern hemisphere sky would not be seen. So, only half of the sky would be seen.

a.) travels faster in solids because the particles are closer together.

air is a gas water is a liquid