Which type of relationship do the parrotfish and the rabbitfish have in the corral-reef environment

The answer is Commensalism. This is a kind of symbiotic relationships, it is an association of organism benefits the others while the other is unharmed. Also it is a relationship between two organisms where the one benefits the other while the other is not affected.

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.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.