<span>Unidirectional flow in the heart is ensured because the heart contains valves that prevent backflow.
These valves keep the flow of the heart going in one direction (hence the name "unidirectional").</span>
<span>The correct answer is b. The open ocean. The definition of an island ecosystem does not have anything to do with water, but simply refers to an ecosystem that exists as a microcosm within a far larger, separate ecosystem. The ocean has lots of separate island ecosystems within it, but it itself cannot be referred to as one.</span>
I believe the answer is family
Answer:
D. Aids
Explanation:
Aids is one of the most deadliest diseases in the world. When you contract aids, it's designed to infect the cells that try to destroy it, it's a whole zombie apocalypse in your body and you don't even know it.
It attacks and weakens the immune system, and our immune system defends our bodies against infections, but HIV is extremely strong and it over powers the system, I'm not sure if there's an immune system strong enough to fight HIV or aids.
The correct answer is A. Petroleum is not a raw material for the production of biofuels. From the name itself, biofuels are obtained from biomass. Biomass are organic materials for example are the choices given in B, C and D.