几个小小的英语问题

1在定语从句中one of 后的先行词若是可数名词的复数,谓语动词就用复数形式,the only one of 后的谓语动词用的是单数形式.
e.g.Tom is one of the boy students in our class who are often late.
Tom is the only one of the boy students in our class who is often late.
2,none of要视具体情况而定,如果后面的名词为复数名词或代词,谓语动词要用复数,如果是不可数名词要用单数,如：
None of us know him.
None of the water is clean
3,a group of 后面一定是加可数名词,即使有时可能你认为不是复数形式,那可能是这个词的单复数同形（比如 people,police等）,谓语动词一般用复数
A group of people are talking outside.
A group of students are playing on the playground.
A group of workers are working in the park.