_

　　8．Jack，you water the flower today，do you?

　　________________________________________________________

　　9．The mother watched her children playing on the beach，with her arms crossing in front of her chest.

　　________________________________________________________

　　10．It might be very difficult to find the cause for the accident.

　　________________________________________________________

　　答案与解析

　　1．Knocking→Knock　句意为：进我的房间之前请敲门。祈使句一般以动词原形开头。

　　2．who→whose　本句为含有定语从句的主从复合句，a couple是先行词，由语境"这对夫妻的孩子很吵"可知children和couple之间是所属关系，故用whose引导定语从句。

3．which→where　句意为：伦敦市中心的交通状况变得如此糟糕，司机们要用50%的时间来排队，以至于当地政府决定就此采取一些措施。句子主干为The situation in central London became so bad...而drivers spent 50% of their time in queues修饰限定前面的in central London，为非限制性定语从句，先行词为地点状语，故应将引导