We have already answered two questions from this ACT social sciences passage about the medieval justice system (back on January 15 and January 19).  Today’s question asks us what “being put to the proof” means in lines 18-19.

The area around lines 18-19 reads:

Excepting trial by battle, only one party was tried or,
more accurately, was put to his “proof.” Proof being
regarded as an advantage, it was usually awarded to the
accused party; in effect he had the privilege of proving
his own case.

Since the accused person is already assumed to be guilty and no one presents sides in a trial (unlike today), the only viable answer is C: he is put to the proof to prove his own innocence.  In fact, the rest of the passage is primarily concerned with methods by which he might prove his innocence.  Today’s legal system might make you empty your bank account, but at least you won’t have to carry hot iron to prove your innocence!