The atria of the heart merely need to allow blood to flow into the ventricle, and therefore aren't very muscular.
The ventricles of the heart need to actually pump blood to the rest of the body, whether to the lungs or the the rest of the body.
One strand runs in the 5 to 3 and the other in the 3 to 5
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It's a ! cnidocytes help in defence and also in capturing prey ! so answer is A !!
B? Im guessing I’m not sure