We're very grateful to the teachers _______ taught us in our primary school.
A:which
B:what
C:who
D:whom
集合in|n∈N*(其中i是虚数单位)中元素的个数是( )
综合题
我国有四大地理区域,下列有关西北地区地理环境特点的叙述正确的是( )