In the following question, four number pairs are given. The number on left side of (–) is related to the number on the right side of (–) with some Logic/Rule/Relation. Three are similar on basis of same Logic/Rule/Relation. Select the odd one out from the given options.
_________ says that the marginal product of a factor input initially rises with its employment level. But after reaching a certain level of employment, it starts falling.