There are two ways to respond to an offer through QTAC: conditionally or outright.
A conditional response allows you to accept your offer while remaining eligible to be considered for higher course preferences in future offer rounds. If you receive an offer for a higher preference in the same semester, your new offer will replace your previous offer.
If you receive an offer for your first preference, you cannot respond conditionally because there are no higher preferences to be considered for. If you want to remain eligible for other courses, you must reorder your preferences before the next offer round.
An outright response (accept, defer or reject) finalises your response to the offer. Once you respond outright, you will no longer be considered for higher preferences in future offer rounds.