Slopes of lines are especially important in economics because a. they measure marginal changes. b. they always tell us something about profits. c. positive slopes are always preferred to negative slopes. d. they always relate to resource and output scarcity.

The correct answer is: A - they measure marginal changes

Explanation:

The term marginal is generally used in economics to refer to the changes in cost or benefits. To measure the changes in marginal costs and benefits, economists tend to use slopes of lines. For this reason, these slopes are considered highly important. Moreover, these slopes of lines are either positive or negative which can be identified by their shape (downwards or upwards).