— The owner of the small shop fought to stop the big corporation from knocking it down.
— Yes, and he finally made it. It was indeed __________.
A:a catch-22 situation
B:a Pandora's box
C:a David and Goliath battle
D:a Jekyll and Hyde existence
下列函数中,在区间0,+∞上为增函数的是( )
生物圈是所有生物的家。它的范围包括( )
设随机变量ξ服从正态分布N(2,9),若P(ξ>c+1)=P(ξ<c﹣1),则c=____ .