The diaphragm in the diagram below is a muscle that contracts during inhalation. thus option A is correct option.
The diaphragm, located below the lungs, is the major muscle of respiration. It is a large, dome-shaped muscle that contracts rhythmically and continually, and most of the time, involuntarily.
Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges.
Learn more about the diaphragm here:
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