Ian, a lawyer, sent an offer to Ray on May 1 offering to sell Ian's car for $5,000. The offer did not contain a provision stating when it would terminate. Under these facts, when will that offer terminate?

A. After a "reasonable" period of time B. After 5 days, as per the "5 day rule" C. The offer will not terminate until Ian or Ray indicate that their willingness to contract has ended D. After 10 days, as per the "10-day rule"