• The correct answer is c) "edge".

The marginal concept, in economics, can be defined as the analysis of adding a little bit of one variable or reducing a little bit of one variable to know the effect on the producers or consumers and determine the best output level. The most common usage of the marginal concept is the analysis of the marginal cost and marginal revenue to maximize profits. Therefore, the term marginal refers to a little change in a variable to find the optimal outcome which can be associated with the word edge that refers to the limit spot before something occurs. In conclusion, the correct answer is option c).

On the other hand, option a) is incorrect because the term marginal is one of the most important concepts in production decisions. Option b) is also incorrect because the word slow is not associated with marginal. Option d) is also incorrect because the concept of marginal analysis is based on a rational decision-making process.