一个位数字为a，十位数字为b，则这个两位数可用代数式表示为 [ ]
A．ab
B．ba
C．10a+b
D．10b+a
答案：D
33．Before she______thethe door, she____what had happened to her computer．
A．walked;noticed
B．walked; had noticed
C．walks; has noticed
D．had walked; noticed
工业企业的材料销售收入、租金收入、运输收入都是企业的( )。
A．主营业务收入
B．其他业务收入
C．补贴收入
D．投资收益
