The straightening movement of muscles at a joint is referred as Extension.
What is straightening of a joint?
Extension – straightening a joint. This occurs when the angle of a joint increases, for example the elbow when throwing a shot put.
What is extension movement?
An extension is a physical position that increases the angle between the bones of the limb at a joint. It occurs when muscles contract and bones move the joint from a bent position to a straight position.
Hence ,option D is correct
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