4.In each of the following groups of words, there are four underlined letters or letter combinations marked A, B, C and D. Compare the underlined parts and identify the one that is different from the others in pronunciation.
A、cool
B、flood
C、food
D、moon
31.
A、If
B、Though
C、Unless
D、Whether
Tom is a careless person. He forgot ____ the door again when he went out yesterday.