How does regular exercise help maintain a healthy respiratory system? A. It helps cilia in the lungs eliminate mucus.
B. It helps lungs from becoming too large.
C. it helps lungs exchange gases at a slower rate.
D. It helps lungs become more efficient at gas exchange.

D

Explanation:

It helps lungs become more efficient at gas exchange.

answer: the first option is not an affect of aging. so the first option is the answer. (secondary sex characteristics appear)

the plates spread at mid-ocean ridges (they are divergent plate boundaries) which allows magma to rise through the weakness between the plates. the magma then emerges as lava from the boundary and cools, creating a new crust.