The total cost curve gets steeper as output increases because of:

A) increasing returns to the variable input.
B) decreasing returns to the variable input.
C) increases in fixed cost.
D) decreases in overhead costs.

The total cost curve gets steeper as output increases because of decreasing returns to the variable input. This means that as the firm produces more, it requires additional units of inputs to produce each additional unit of output, which leads to increased costs. As a result, the cost curve becomes steeper. In other words, as output increases, the marginal cost of production increases, which in turn causes the cost curve to get steeper.