Answer:
Incorrect pronoun: they.
Correct sentence: If a student feels ill, he -or she- should be sent to the nurse.
Step-by-step explanation:
A pronoun shift is a type of grammatical error in which the author uses a given pronoun at the beginning of the sentence or paragraph and then suddenly changes to another pronoun and, therefore, confuses the reader. This shift can include changes in persons -first, second or third- or between plural and singular.