If you want to join us,you _______ help kids with their scho

I'm pretty sure the answer is C.you could help kids,it is polite and suggesting means you can help kids with their schoolwork.
B and D are requesting,means must,we can eliminate those two.A-would means will,which does not fit in this sentence.

应该选“A”希望可以帮到您`(*∩_∩*)′~~~~

I'm pretty sure the answer is C. you could help kids, it is polite and suggesting means you can help kids with their schoolwork.
B and D are requesting, means must, we can eliminate those two. A-would means will, which does not fit in this sentence.

D.should 应该