You need to answer a given question containing a blank (_). Your answer must be one of the two objects mentioned in the question, for example "trophy" and "suitcase". Your answer must not contain a word that is not present in the question. Please don't use articles (e.g., the, a) before the answer.

The essay on microbiology was more interesting than the one written on statistics. _ must be an interesting subject.
microbiology

The battery ran out slower on the phone than the iPad because the _ was older.
iPad

The caterer removed food from the containers and put it on the trays until the _ were full.

trays