What starts an involuntary swallowing action when it senses food

There are three phases in swallowing which include voluntary and involuntary ways. The oral phase is a voluntary swallowing happens after the mechanical digestion of food and the use of saliva. of food that uses special nerves that signal and help food to be pushed further in the pharynx and then to the esophagus.    The pharynx starts an involuntary swallowing action when senses food. 

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The answers are out a and b