What keeps the blood flowing in one direction?

With this system, blood always flows in only one direction inside the heart. There are also valves at the bottom of the large arteries that carry blood away from the heart: the aorta and the pulmonary artery. These valves keep the blood from flowing backward into the heart once it has been pumped out.

Explanation:

my hamster died and my second hamster i got after that one died as well. i also lost two birds named rainbow and kiwi, (they didn't die, they flew off and escaped). i lost a cat named omi, and a dog named snoopie. the best way i got over it is, paying my respects, and just thinking that they were in a happy place. as well as just remembering but not thinking about it all the time, just do fun activities and try not to think about it too much. hope you feel better. i'm sorry about your loss. : (

i don't think so because different teachers have different materials. tehy teach differently, unless you know for sure your teacher is the exact same as others. i would just contact ur teacher