both:两个都(用于肯定)
each:每个(表个体)
Every:每个(表全体)
neither:两个都不(用于否定)
either:1).或者(用于选择)常与or 连用
2).也(表相同)(用于否定)
e.g.:
1.Both the students are girls.
2.Each student has a pen.
3.Neither the student is from London.
4.Either he or she has a pen.注：has是被she 限定的,意思就是说,动词的形式与or 后面的主语一致.
例如,Either he or I have a pen.
He doesn't have a pen,she doesn't have,either.