How did dregg do on his antarctic test math answers?

The answer is Dregg did delightfully on his Antarctic test because ... he knew it cold! This puzzle is a play on words; when somebody is fully set for every answer on a test, they can be said to "know it cold." At the same time the Antarctic is recognized for being, in fact, very cold. So in this joke Dregg knew all the answers about the cold weather of the Antarctic.