1.He is one of the boys who always _do_ well at school.
2.He is the only one of us who _has_ passed the exam.
3.Either you or one of your syudents _is_ to attend the meeting.
4.At present ,one of the arguments in favor of the new airport _is_ that it will bring a lot of jobs to the area.
5.Every student as well as teachers who are to visit the museum _is_ asked to be at the cshool gate on time.
分别解释一下横线上为什么填这个（主要是为什么谓语动词填单数或复数）,