Which of the following expenses is deductible as an entertainment expense? 

a. The depreciation on an airplane used to entertain customers. 

b. The cost of a hunting camp used to entertain customers.

c. The dues of a racket club used to keep in shape. 

d. The cost of a paintball party for clients paid for by a computer salesman at a computer fair. 

e. None of these are deductible.