Answer the following question given this paragraph: 

Capillaries are the smallest type of blood vessels. They connect the smallest arteries (arterioles) and veins (venules). Exchange of substances between cells and the blood takes place across the walls of capillaries, which may be only one cell thick.


Q: What is the term for the smallest blood vessels?

 Choices:

- muscles

- Aortas

- arteries

- capillaries

A:
capillaries
