Directions: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 iden-tdtify the one that is different from the others in pronunciation.Mark your answer by blackening the corresponding letter on the Answer Sheet.
A、combination
B、climbing
C、bamboo
D、ambition
54.What does the underlined word“trilogy”in Paragraph 4 mean?