Please answer the following question by reasoning step-by-step.
What breathes by relaxing the lungs?\nOptions:\n- (A) mammals\n- (B) tortoises\n- (C) dogs\n- (D) chickens\n- (E) ducks\n- (F) humans\n- (G) crocodiles\n- (H) animals

(A)
Mammals breathe with the help of a diaphragm.

Belly breathing uses the diaphragm, which helps relax the lungs.

Mammals breathe by relaxing the lungs.

.

So, the answer is (A)