How Did Frederick William I, King of Prussia, Sustain Agricultural

How did Frederick William I, king of Prussia, sustain agricultural production while dramatically expanding the size of his army?

A) He required women to work in the fields when their husbands served in the military.
B) He purchased African slaves to sustain agricultural production while Prussian men trained for the military.
C) He ordered all Prussian men to undergo military training, after which they could return home and serve as army reservists.
D) He required monks, priests, and other clerics to perform agricultural work when needed by local nobles.