题目内容：
(21)__________参考答案：
答案解析：
简答题：(21)__________
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Air-service is too__________to be used frequently.
Air-service is too__________to be used frequently.A．fast B．dangerous C．expensiv
You will hear a long dialogue on launching a new programme.
You will hear a long dialogue on launching a new programme.For each question (
第34题答案。
第34题答案。A．unil B．when C．while
20___________
20___________
14___________
14___________