In Which Case Is the Offer Still Valid at the Time

Multiple Choice

In which case is the offer still valid at the time the acceptance is made?

A) Hal offered to sell a book to Sid. Hal died, and Sid sent an acceptance two days later.
B) By-Waste Co. telephones XXX Co. offering to dispose of XXX Co.'s chemical waste by a particular method. XXX says it has another way to dispose of the waste. Then XXX finds out the method it planned to use violates environmental protection statutes, so it sends a letter of acceptance to By-Waste.
C) Ray offers to sell his AT&T stock for a particular price by May 1. On May 2, Kathy agrees to buy the stock.
D) In a face-to-face transaction, Pat offers to sell Mike his stereo and Mike accepts.
E) All of the above.