Many people do not realize the importance of health __________ they have fallen ill.
A:since
B:until
C:while
D:after
下列关于日本的叙述,错误的是( )
____ ____Mr Brown____to London?
- _____you sing English songs yesterday?
- No,I didn't. ( )
已知y=f(x)为R上的可导函数,当x≠0时,f′(x)+fxx>0,则关于x的函数g(x)=f(x)+1x的零点个数为( )