Silvia Has Received an Offer from Cam to Purchase Her

Silvia has received an offer from Cam to purchase her touring bicycle for $1500.She emails Cam and accepts this offer.Cam is away from his computer and does not see the acceptance until three days later,by which time he has purchased a different bicycle.Cam had emailed the original offer to Silvia.Included in that email was the requirement that she by email.

A) Cam is obligated to purchase the bicycle because he designated the use of email and so acceptance occurred when Silvia's email reached his system.
B) Cam is not obligated to purchase the bicycle because he has purchased another one.
C) Cam is obligated to purchase the bicycle because he did not revoke his offer prior to acceptance.
D) Cam cannot accept the offer via email because email cannot be used in the formation of valid contracts.
E) a and c.