——Mr. Li will check our homework this afternoon. ______ you _______ it?——Not yet. I'm doing it right now.
A:Do, finish
B:Had, finished
C:will, finish
D:Have, finished
They're pictures of different ____in China.(place/places)
已知关于x的一元二次方程x2-4x+1=0的两个实数根是x1、x2,那么x1+x2=____.
亚洲河流呈放射状分布的原因是 ( )