请英语高手解答有几个语法题

题目

请英语高手解答有几个语法题
改错（我想知道的是为什么那么改）
1.A large number of land has been covered by deserts.（答案是把number改为amount）
2.1.A large number of land has been covered by deserts.（答案是把number改为amount）.（答案是second前面加a）
3.She is the second to none in her studies.（答案是去掉the）
我想知道选择的选项选它的原因是什么
4.We always keep _______spare paper,in case we ran out.
A.too much B.a number of C.plenty of D.a good many
5.He did it _it took me.
A.one-third a time B.one -third time C.the one-third time D.one-third the time
6.It is reported that the US uses_________energy as the whole of Europe.
A.as twice B.twice much C.twice as much D.twice much as
7The house you bought is_____mine.
A.as three times as B.three times the size of C.three times the size than D.as big as three times than

答案

1 a large amount of 修饰不可数名词；
2相同
3 second to none=the best 加the 表顺序,无此意
4 plenty of 修饰可数和不可数,too much不合题意
5d 他只花费了我所用时间的三分之一就完成了它；
6c固定用法
7b 固定用法