Which of the following is true regarding acceptance?
a) in the absence of a provision in an offer regarding how acceptance is to be made, acceptance is effective upon dispatch into a mailbox.
b) acceptance is never effective until it is received.
c) an offeror may not by law specify that an offer can be accepted only by facsimile to a stated fax number and that the acceptance is not effective until actually received.
d) an offeror may revoke an offer as long as the revocation is made before an acceptance is received.