Answer:
If a student wants to drop a class after the drop date, he or she must get permission from the associate dean.
Step-by-step explanation:
In this case there are two sentences linked by a comma. One is subordinate to the other, that is to say, the first one is a adverbial clause of condition and depends on the other clause which is independent. In the first example, the subject of the sentece is "student" (a neutral noun which has no genre), whereas in the second one we need to identify the genre of the subject, so we have to include both male and female possibilities, that is to say, he or she.