17. When exercising the muscles in one’s back, it is important, in order to maintain a healthy back, to exercise the muscles on opposite sides of the spine equally. After all, balanced muscle development is needed to maintain a healthy back, since the muscles on opposite sides of the spine must pull equally in opposing directions to keep the back in proper alignment and protect the spine. Which one of the following is an assumption required by the argument?

Вариант ответа 1 - (A) Muscles on opposite sides of the spine that are equally well developed will be enough to keep the back in proper alignment.

Вариант ответа 2 - (B) Exercising the muscles on opposite sides of the spine unequally tends to lead to unbalanced muscle development.

Вариант ответа 3 - (C) Provided that one exercises the muscles on opposite sides of the spine equally, one will have a generally healthy back.

Вариант ответа 4 - (D) If the muscles on opposite sides of the spine are exercised unequally, one’s back will be irreparably damaged.

Вариант ответа 5 - (E) One should exercise daily to ensure that the muscles on opposite sides of the spine keep the back in proper alignment.