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
Tom is a careless person. He forgot ____ the door again when he went out yesterday.
A、to lock
B、locking
C、to have locked
D、having locked
Pets____constant care are not suitable for people with little spare time.