5.(2019河北廊坊期末统考) Above their home, there lived a couple, 　　    children often made a lot of noise.    

答案　whose    句意:在他们家的楼上住着一对夫妇,那对夫妇的孩子经常制造很多噪音。先行词为a couple,将先行词代入定语从句后为:The couple's children often made a lot of noise.由此可见,关系词在定语从句中作定语,故答案为whose。

6.(2018浙江宁波5月模拟,59)Every day, the Americans throw away 500 million plastic straws,     　     are enough to circle the earth twice.

答案　which　此处所填单词引导非限制性定语从句,修饰前面的500 million plastic straws, 因此用which。