Which of the following sentences from the article BEST develops a central idea of the
article?
A) Simply stated, factors of production are the inputs necessary to obtain an output.
B) The income deriving from the ownership of
land is known as economic rent.
C) The human effort that qualifies as labor may
be either manual or mental.
D) The owners of capital receive their income in
various possible forms; profits and interest are the usual ones.