Answer:
d. I need to leave for school right now; however, I don't have all of my school supplies gathered.
Step-by-step explanation:
However in this case is used to as a conjunctive adverb so a semicolon is required before "however" in order to show there are two different sentences conjoined by an adverb. The first sentence is a fully independent clause that's why it is required a semicolon to separate it from the other clause. Then, after however it is required a comma.