[ ]Tina and Julia working hard at their lessons

问题描述:

[ ]Tina and Julia working hard at their lessons
a.Is b.Do c.Can d.Are
[ ]里面应该填哪一个
为什么
为什么不能用do呢

现在进行时:
sb.is doing sth.
sb.are doing sth.
而且又是复数,所以必须用 are.