On Monday morning, Masako faxes her offer to Erik.On Monday afternoon, Erik writes, "I accept" on the fax.On Tuesday morning, Erik mails his acceptance.On Tuesday afternoon, Masako faxes Erik a revocation of the offer.On Thursday morning, Erik's acceptance letter arrives at Masako's office.

a. the offer was revoked when the revocation was faxed because it was sent before the acceptancearrived at Masako's office.

b. the contract became valid when Erik wrote, "I accept" on the fax.

c. the offer was revoked when the revocation was received by Erik because it arrived before theacceptance arrived at Masako's office.

d. the contract became valid when Erik mailed the acceptance.