Neither my sister nor I ___________ been to America before.
A:have ever
B:have never
C:has ever
D:has never
—How much do I o____ you, Sir?
—Well, it's $5.50 plus tax. Thank you.
已知抛物线y=x2+3x+c经过三点2,y1,-3,y2,-1,y3则y1,y2,y3的大小关系为( )
世界上唯一没有定居居民的大洲是( )