Which will most likely cause a decrease in the predator population? an increase in prey populations 2. a decrease in prey populations 3. a decrease in decomposers 4. an increase in producers.

Explanation:

Predators are those animals which hunt prey. Prey is the animals which is "hunted".

When the prey population is less (a decrease in prey population), There will not be more animals for "predators" to hunt and so, the competition of living will become more. Decrease in preys population would lead to a decrease in predator's population because many predators will die of hunger.

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they deliver oxygen to the blood

i believe the answer would be b. hope it : )