The mechanical digestion in the stomach involves the contractions of muscle smoothly. Thus, the correct answer is C.
What is digestion?
The process of converting food into nutrients to use it as energy and for development is called as digestion. The digestion takes place mechanically and chemically.
In the chemical process of digestion, food is broken down with the help of enzymes whereas in the mechanical process of digestion food is broken down with the help of chewing from teeth or tearing.
Therefore, option C is correct as this breakdown through teeth involves contractions and relaxation of muscles.
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