Alfred Marshall's Concept of "Transfer Earnings" Denotes

Alfred Marshall's concept of "transfer earnings" denotes

A) the value of the factor to its user.
B) a return to a particular factor which must be the same for all uses of that factor.
C) the amount a factor earns over and above what is necessary to keep the factor from transferring to an alternative use.
D) the amount that a factor must earn to keep it from transferring to another use.
E) the amount the factor earns every time it transfers between locations.