Which term describes any relationship in which two species live closely together?

The correct answer is -

Symbiosis.

Explanation:

Symbiosis can be described as close biological interaction between two organisms belonging to the same or different species. There are different types of symbiotic relationships such as mutualisms, parasitism, and commensalism.

Example - lichen represents mutualistic relationship between photosynthetic organism such as algae and a fungus.

Thus, symbiosis is the right answer.

explanation:

on disadvantage of hydroelectric power is the cost. another disadvantage of using hydroelectric power is finding a water source powerful enough to harvest hydroelectric power.

the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.