Which of the Following Sentences Is Not Grammatically Correct

Which of the following sentences is not grammatically correct?

A) The data was analyzed with a t-test.
B) Since the earliest days of psychology, many researchers have discussed the nature of the self.
C) When a student is not prepared for a test, he or she is likely to feel anxious.
D) As participants entered the lab, they received a packet of questionnaires.