Critical Reasoning (CR) | Re: When exercising the muscles in one’s back, it is important

Premise: 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.
Conclusion:balanced muscle development is needed to maintain a healthy back
Premise: 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?

(A) Muscles on opposite
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