3 For the following questions, select the key term that best matches with the definition provided. - A cost for which there is no cash outlay at the time a resource is being used, or for which no cash payment is required - A planning concept relating to the proportion of a firm's inputs that may be fixed or varied in a given time period. - A time period long enough that all factors of production can be varied - The change in total cost when output is changed by one unit - The amount added to total revenue when an additional unit of output is produced and sold A. Length-of-run B. Implicit costs C. Long run D. Marginal cost E. Marginal revenue