Which of the following would constitute an offer?

Explanation

Offers include bids on an auction and a price proposal that is valid for 14 days. The other three options are Invitations to Treat. See p.3 for the full list of what constitutes an Invitation to Treat. The tricky thing here is that an auction is an invitation to treat but a bid on an auction is an offer. An auction is an ITT because you're encouraging people to make an offer to you. A bid on the auction is the offer (you offer to buy something at a price you propose).