作业帮The boy failed the exam again,and ____ cost his parents many sleepless nights为什么用that,不用which
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The boy failed the exam again,and ____ cost his parents many sleepless nights为什么用that,不用which
The boy failed the exam again,and ____ cost his parents many sleepless nights
为什么用that,不用which
The boy failed the exam again,and ____ cost his parents many sleepless nights为什么用that,不用which
that 在这里是个指示代词, 代替前文The boy failed the exam again这回事
因为有并列连词and, 不可能把后面一句理解为定语从句, 所以不可能用关系代词which
如果用which, 除非把and 去掉
The boy failed the exam again,【which】cost his parents many sleepless nights
这里因为有了and，这句话就是并列句，所以后面是主语+谓语：这里的主语是that，指代前面所提的内容（The boy failed the exam again, )
如果要用which，那么就去掉and， 让which引导的从句成为非限制性定语从句。
and连接的是两个并列句，所以用that指代上文提到的事情，前后两句是并列关系。
而which连接的是定语从句，跟前面是主句和从句的关系，所以不符合。
换句话说，去掉and，用which不用that。
问题在【and】上。
注意：连词后面不是定语从句。
连词是连接两个并列句子。本句如去除【and】,选which，为定语从句。