6. Capillaries are how many cell thick?
- three hundred and ninety four
- five
- two
- one
- ten
7. What carries blood to the heart?
- Capillaries
- Arteries
- Veins
- unicorns
8. Veins have what?
- Small lumen
- Valves
- thick layers of muscle
9. Arteries carry blood to the heart
- false
- true
