第14题: [单项选择]They have been waiting for many hours. The airplane must have been ______. A. of schedule B. on schedule C. ahead of schedule D. behind schedule 参考答案:D 答案解析:本题测试介词短语的用法。根据题意，是指航班晚点，故应选behind schedule“落后于预定计划”。of schedule搭配不存在；on schedule“按时”；ahead of schedu
第15题: [单项选择]Since the middle of this century ______ has been learned about space than in all human history before that time. A. much B. more C. better D. a lot 参考答案:B 答案解析:[精解] 本题考查代词。分析句子后发现句中有than说明这是一个比较级的句子。题干中缺少主语，虽然better是比较级形式，但它是形容词，不能作主语。more是much的比较级，可以作主语。所以本题的
