第15题:[单选题]It is imperative that students ____________ their term papers on time. A.hand in B.would hand in C.have to hand in D.handed in 参考答案:A 考查虚拟语气。句意为“学生必须按时上交他们的学期论文”。在“It is imperative/necessary/important/required/advised等表示命令、必要、要求、建议等意思的形容词或分词+主语从句”的结构中,从句谓语动词用虚拟语气,should+动词原形,should可省略。故选A。