Doug offers to sell a computer router to Eve, but it is stolen before Eve accepts. Doug:

a. is not required to obtain a similar item for Eve, because it could take an unreasonable period of time to obtain a replacement.
b. is not required to obtain a similar item for Eve, because the theft of the original router terminated the offer.
c. must obtain a similar item for Eve, if Eve offers to pay before delivery.
d. must obtain a similar item for Eve, if Doug tells Eve that he accepts the offer.