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
(31)___
A、How
B、Whether
C、Before
D、As
18.Children don't understand initially what they are reciting, but___it will have an impact on their thinking.