Mary offers to buy Hal's desktop computer for $400. Hal sends Mary an e-mail of acceptance. The $400 is to be paid upon Hal's delivery of the computer. Which of the following properly classifies this contract?A. This is a bilateral, valid, executory contract.B. This is a bilateral, valid, executed contract.C. This is a unilateral, express, executory contract.D. This is a unilateral, implied-in-fact, executed contract.