How Does Contract Growing of Chickens Make Serfs of Family

How does contract growing of chickens make serfs of family farmers?

A) Major chicken production companies buy up small farms and evict owners.
B) Chicken corporations own the birds, while farmers raise them en mass under contract.
C) Farmers raise birds on a small scale, but these are rapidly aggregated by large corporations.
D) Large corporations count on small farmers to determine growing conditions and production rates.