备件周转率的推荐值是()
A、1~3次/年
B、2~4次/年
C、3~5次/年
D、6~8次/年
参考答案:D
I'm not sure whether he has finished writing the book, but he ____ it last month. [ ]
A. worked at
B. was working on
C. worked on
D. was working at
静态成员函数可以直接访问类的______成员,不能直接访问类的______成员。