This is an involuntary, non-striated muscle found throughout the human body.

Smooth muscle

Explanation:

I got it wrong on usatestprep and when it showed me the answer key, smooth muscle was the correct answer.

i think that the best answer would be c.

tell me if im wrong : )

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."