Many adjustments take place in and around the muscle cells as a result of
training, and as with adapting heart muscles, relatively slow, easy running
does an excellent job of promoting the desired results.

(A) adapting heart muscles, relatively slow, easy running does an excellent job of promoting

(B) adapting heart muscles to relatively slow, easy running, which excellently promotes

(C) adaptations to the heart muscle, relatively slow, easy running does an excellent job of promoting

(D) adaptations to the heart muscle, running slowly and easily does a relatively excellent job of promoting

(E) heart muscles that adapt to relatively slow, easy running, which do an excellent job of promoting