Swimming is a good way to keep health.

　　Who is her father is not known.

　　4. 集体名词作主语时

　　a) mankind/humanity/man（人类）作主语的时候，谓语动词一般用单数形式

　　Only man knows how to cook.

　　b) 由people, police, cattle, youth等集体名词作主语的时候，谓语动词用复数形式

　　The cattle are grazing in the field.

　　c) Family, croud, class, public, enemy等集体名词作主语的时候

　　i. 若当整体看，则谓语动词用单数形式

　　Our class is very diligent.

　　ii. 若他们表示的人或者事物当作若干个个体来看，谓语动词则用复数形式

　　When I came into the room, his family were watching TV.

　　iii. A family/group/class作主语时，谓语动词用单数

　　families/groups/classes作主语时，谓语动词用复数

　　A group is coming to the zoo.

　　5. 其他情况

　　a) 主语为表示距离、时间、长度、价值、金额、重量等复数名词的时候，谓语动词用单数形式

　　3 kilometers is not very far.

　　Three times three makes nine.

　　b) one, every/each one, each, anyone, either, neither + of + 复数名词

　　谓语动词一般用单数形式，因为of之后的复数名词不是主语而是介词of的宾语，of前面的one, every one … 才是主语

　　Neither of them is right.

　　Each of them has a slide.

　　c) none of + 不可数名词——谓语动词用单数形式

　　none of + 可数名词　——谓语动词单复均可

　　None of that money in the desk is his.

　　None of his classmates knows the truth.

　　d) 分数或百分数 + of + 词组

　　分数或百分数+ of +词组作主语时，谓语动词的数取决于of后的名词或者代词的数；若名词或代词是复数，谓语动词用复数，若名词或代词是单数，则谓语动词用单数

　　Three-thirds of the surface of the earth is sea.

　　Tens of tons of waste goes into the air with the smoke every day.

　　e) more than one +(单数名词)+单数动词

　　more than two +(复数名词)+复数动词

　　More than one white rose has bloomed.

　　More than two white roses have bloomed.