Four days ago, Ulf saw a pop-up ad on his phone that said "Best deal in town! Laser Printer - $450!" When he went to the store this afternoon and said he wanted one, they replied that they didn't have any left, nor could they get one. On these facts, which of the following is true?

a) Ulf could sue them for breach of contract because he was accepting their offer.
b) The wording in the pop-up ad was merely an invitation to treat, made to the public, and no contract was formed.
c) Ulf can successfully sue the store for breach of an option contract.
d) The offer by the store had lapsed before he tried to accept.
e) The store had revoked the offer before he tried to accept.