In a class, there are three classmates A. B, and C who participated in the Olympiad and each won one, two, and three prizes. The class teacher guessed that: A must be the first prize, B must not be the first prize, and C must not be the third prize In fact, the head teacher only guessed one. Based on this, it can be inferred who won the second prize? ['Classmate A.', 'Classmate B.', 'Class C.', 'Unable to judge.']