What is the difference between a fixed cost and a variable cost?

a A fixed cost does not change when output changes, whereas a variable cost does.

b A fixed cost includes all costs associated with production. A variable cost only includes the extra cost of producing one additional unit of production.

c A variable cost includes all costs associated with production. A fixed cost only includes the extra cost of producing one additional unit of production.

d A fixed cost changes when output changes, whereas a variable cost does not.