- Tom, you look tired this morning. What's wrong?
- I was busy and I didn't go to bed _________ 12 o'clock last night
A:until
B:when
C:though
D:unless
设函数f(x)在x0处可导,则lim△x→0fx0-△x-fx0△x等于( )
下图漫画说明生命科学面临的难题是( )