A:how they were excited
B:how excited they were
C:how excited were they
D:they were excited
李林同学在不同季节的制作过程中,一定发生了化学变化的是( )
(Ⅰ)证明:BC⊥面PAB
(Ⅱ)求侧棱PC与底面ABCD所成的角.
设函数fx=2-x-1,x≤0x12,x>0,若f(x0)>1,则x0的取值范围是____