第5题: [单项选择]You ______ all morning, but you ______ three letters! A. have been typing, have only done B. were typing, only did C. had been typing, have only done D. have typed, have only done 参考答案:A 答案解析:all morning表示一个时间段，应用现在完成进行时。后半部分强调的是结果，整个上午的时 间里做了多少事。
