Answer the following question given this paragraph: 

While the egg is developing, other changes are taking place in the uterus. It develops a thick lining that is full of tiny blood vessels. The lining prepares the uterus to receive a fertilized egg if fertilization actually takes place.


Q: While the egg is developing, other changes are taking place in the uterus. it develops a thick lining that is full of what?

 Choices:

- large arteries

- white blood cells

- amniotic fluid

- tiny blood vessels

A:
tiny blood vessels
