Both the parents and the children are here.
ii. A、B表示同一个人、物或者观念的时候，谓语动词要用单数形式
A journalist and author lives in the sixth flat.
The turner and fitter is under twenty-five.
iii. And连接几个单数主语，主语由each、 every、 no、 many a等词修饰的时候，谓语动词要用单数
Each boy and each girl is invited.
Every boy and girl is invited.
No boy and no girl is there now.
iv. A、B为两个不可分的东西时，谓语动词用单数
A law and rule about protecting environment has been drawn up.
Bread and butter is nutritious.
b) 由or, not only… but also …, either… or …, neither… nor …连接主语时，谓语的人称和数与靠近的主语一致 （注意，叙述句和疑问句随语序不同而不同）
Either you or I am mad.
Neither you nor he is naughty.
Not only the farmer but also his family were friendly to me.
c) 当主语后跟有with, along with, together with, besides, except, like, including, as well as, rather than等词的时候，谓语动词不受词组的影响，仅和主语保持一致
All but one were here just now.
A library with five thousand books is offered to nation as a gift.
2. 单一主语的情况
a) 以复数形式结尾的统称名词作主语时，例如physics, maths, economics, news, means, works, 等一般在谓语动词中用单数形式, 当然，若表示复数的意思则另当别论
Physics is very important.
Every means has been tried.
b) 当由至少两个部分组成的工具的名称，或者衣服的名称等作主语时，例如trousers/pants, shoes, glasses, scissors, goods, clothers等，谓语用复数形式；如果这些词由Pair(suit, piece, series,kind)+ of修饰的时候，谓语动词要用单数
My trousers are white and his clothes are black.
A pair of scissors is lying in that drawer.
但是在these/those pairs (…) of + 复数名词之后，谓语动词则用复数形式
These kinds of glasses are popular this summer.
http://english.xuezhishi.net/groundwork/grammar/2007-01-23/3370.html
