In all but one of the following situations, the contract is frustrated. Identify the exception.
a. Jack contracts with Bill to build a barn on his one acre lot but before the permit is obtained, a new law prohibits barns on less than three acres.
b. Rudolph is due to appear in a local variety theatre which has just been destroyed in a fire of unknown origin.
c. Frank has contracted to ride Emperor, a prize horse in the Canada Day races on July 1, but on June 28 the horse breaks a leg and has to be destroyed.
d. Jerry, a doctor, is due to perform a heart transplant operation on Mary and the night before the surgery his arthritis becomes so painful that he cannot hold a scalpel.
e. Gregory, a trucker with whom you contracted last month to haul potatoes tomorrow, phones to tell you that his truck has broken down.