Question

select the infinitive or infinitive phrase.
if you sit with your legs crossed or your feet under you for too long, your feet may start to tingle. this sensation, called paresthesia, is caused by pressure on the nerves.

Explanation:

An infinitive phrase starts with the base form of a verb preceded by "to". In the given text, the only phrase fitting this structure is the part that functions as the complement to the verb "start".

Answer:

to tingle