In the United States, as of 2018, Federal Prison Industries

In the United States, as of 2018, Federal Prison Industries employed 12,000 inmates at 83 factories, and paid them between 23 cents and $1.15 per hour. What explains the low wages of prison workers?

A) Prisoners are few in number.
B) Wages in the free labor market are high.
C) Market power of prisons over prisoners.
D) Prisoners get free food and accommodation.