Which of the folloiwng cost can never be zero? (1)
(a) Total variable cost (b) Marginal cost
(c) Average variable cost (d) Average Fixed cost

Dear student , 

Answer is (d) Average fixed cost 
(Because , Average Fixed cost always remain positive as when the output increases Average Fixed cost decreases but always remain positive . As, Average fixed cost is equal to (Fixed cost / output). )

Regards.