Consider a Firm Producing Skateboards in One Factory

Consider a firm producing skateboards in one factory.In determining this firm's value added to national income,we would start with its total revenue and subtract the cost of (among other things)
1) salaries to the firm's cleaning staff;
2) electricity used in the factory;
3) the wood used for the base of the skateboards.

A) 1 and 2
B) 2 and 3
C) 1 and 3
D) 1 only
E) 3 only