参考答案:computers and Internet have become an indispensable part of our society 答案解析:[解析] “必不可少的”可译成necessary，但在此indispensable符合语境，结合句意和汉语部分的“已经”可以确定所译部分的谓语动词用现在完成时。
第31题: [单项选择]What did he do A. He telephoned me. B. He picked up the phone. C. He put the receiver down. D. He put my hanger up. 参考答案:C 答案解析:电话场景，固定搭配。根据原文“He hung up on me．”，关键在于理解固定搭配hang up。hang up：to end up a telephone conversation，意指：挂断
