购买单价为a元的作业本n个，付了b元，应找回（ ）元 [ ]
A.（b-a）
B.b-n
C.na-b
D.b-na
答案：D
最大的四位数和最小的三位数它们之间相差（ ）。
The reporter didn't go to bed until he finished ______ the article.[ ]
A. writing
B. write
C. to write
D. wrote
