One tightens and the other relaxes to make the bones move. Hence, option A is correct.
<h3>What are muscles?</h3>
A muscle is a group of muscle tissues which contract together to produce a force. A muscle consists of fibres of muscle cells surrounded by protective tissue, bundled together with many more fibres, all surrounded by thick protective tissue.
Muscles work in pairs, when one muscle shortens the opposite muscle lengthens e.g. the biceps shortens to bend the elbow at the same time its opposite muscle, the triceps, lengthens to allow the movement to occur. Good working between pairs of muscles allows for smooth controlled movement.
One tightens and the other relaxes to make the bones move. Hence, option A is correct.
Learn more about the muscles here:
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