— did you stay in the library?
— I stayed there for over two hours.
A:How long
B:How often
C:How many
根据上下文选择合适的疑问词,补全对话
How old, what, who, where, when, whattime
被称为“经济联合国”的世界贸易组织(WTO),构建了当今世界的多边贸易体制。其前身是1947年成立的关税与贸易总协定,当初成立这一组织是为了
正切函数y=tan(2x﹣π4)的定义域是( )