问题
选择题
The number of air crashes that ________in developing countries ________increasing. [ ]
A. happens; is
B. happen; is
C. happens; are
D. happen; are
答案
答案：B
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The number of air crashes that ________in developing countries ________increasing. [ ]
A. happens; is
B. happen; is
C. happens; are
D. happen; are
答案：B