Where was the hydrogen that is found in the Sun created?

A friend takes a ride on a spaceship to a distant star and returns to Earth.  You and your friend were the same age when your friend left on the spaceship. When your friend returns she

What is the nature of most of the matter in the universe?

This is not a formed element of the blood.

Thymosin is a hormone that plays a role in:

The cavity of the heart that normally has the thickest wall is the:

Chordae tendineae are associated with which structure(s)?

The hormone that causes ejection of milk into the mammary ducts is:

A nova is believed to occur when which of the following pairs of stars are in a binary system?

If this valve were damaged, it could allow blood to leak back into the left ventricle.