第13题: [单项选择]Clearly, if we ______ in the class we must communicate with our classmates. A. participate B. are to participate C. will participate D. do participate 参考答案:B 答案解析:本句是动词不定式放在be动词后面做表语,表示1)计划要做的事;2)有义务要做的事;3)(在条件句中指)预期要达到的目标;4)(如果是用be动词的过去式was/were to do)证明了事情发展的结果