唐太宗被各少数名族称为“天可汗”,其中最主要的原因是( )
A:唐朝国力强大
B:唐太宗实行开明的民族政策
C:唐太宗本人的素质很高
D:唐朝的经济繁荣
已知函数fx=x+sinxx∈R,且fy2-2y+3+fx2-4x+1≤0,则当y≥1时,yx+1的取值范围是( )
You'd better ask a ______, such as your aunt or sister, to look after your children while you are away.