15.The professor insisted that we ___ our papers on Monday.A.handed in B.will hand in C.hand in st hand in26.The river is dangerous for children ____.A.swimming B.swimming it swim swim in当然要的不是仅是最后答案，我想知道为什么这么选，请大家讲解的详细些，谢谢大家。
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15题选C原因是insist（坚持，执意）这样的词带有虚拟语气，后面的动词必须是原形。26题选D原因是be dangerous for sb to do sth.在河里游泳，是swim in the river
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c insist 后接虚拟语气should +动词原形,should可以省略。D 固定句型be+ adj.+(for sb.) to do sth. 在河里游泳用in
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15.Theprofessorinsistedthatwe___ourpapersonMonday.A.handedinB.willhandinC.handinsthandin选c,在insist引导的从句中常用should+动词原形的虚拟语气,且should可以省略,所以这里用原形;26.Theriverisdangerousforchildren____.A.swimmingB.swimmingitswimswimin选d, do做定语toswim和theriver之间有动宾关系,因为是在河里游泳,故选择swimin。
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sist后跟shoulddosth.答案中should省略 his+ rsbtodosth,固定表达。不选c因此swim是不及物动词,表示在河里游泳要加介词in