Alicia and Robert are evaluating their company's contract policies for offers and acceptances. Which of the following describe an acceptance of a contract offer that is not valid? Select all that apply.

A seller receives an offer for the sale of their house and responds with an acceptance by mail within the specified timeframe.

A buyer receives an offer for the purchase of a car and responds with an acceptance via email, but the email is sent after the offer expires.

A contractor receives an offer to build a house and responds with an acceptance, but the response includes additional terms not mentioned in the original offer.

A tenant receives an offer for a lease agreement and responds with an acceptance in person, but the landlord has already withdrawn the offer before the acceptance is communicated.