Why does henry david thoreau think imprisonment is
a. because governments can only lock a person up physically, not mentally
b. because prisoners know that governments dont have true authority to lock them up
c. because prisoners tend to train one another on how to commit crimes
d. because prisons only serve to make prisoners hate the government more

Ah, I remember Thoreau very well, to the point I was sick of him actually. The answer would be A, he believed being imprisoned (even if only for a single night) merely kept his body in place. His mind was still free and imprisonment only further fueled his philosophical thinking, if you can call it that. Heads up though, next time you should include what text the question addresses.