Answer & Explanation
D) Direct Materials
Direct Materials doesn't come under Fixed Cost because it vary with changes in the activity level of a business.
Fixed Cost :
A fixed cost is a cost that does not change over the short-term, even if a business experiences changes in its sales volume or other activity levels.
It is of some importance to understand the extent and nature of the fixed costs in a business, since a high fixed-cost level requires a business to maintain a high revenue level in order to avoid generating losses.
Examples of Fixed Cost are:
Insurance, Salaries, Rent, Property Taxes,...