Veins contain a network of values to ensure a one-way flow of blood but arteries do not. this is because veins must counteract the force of on blood flow.

1. and 2. question: in which equation? or i don't understand you, 3. a), 4. c), 5. c), 6. b), 7. d), 8. d) if small number is underlined(behind symbol) , b) if big number is underlined(in front of symbol)9. what is underlined there? 10. c)

Hello.the answer is  hydrosphere, geosphere, and biosphere  have a nice day