1） 在代詞what, which, who, none, some, any, more, most, all等詞的單複數由其指代的詞的單複數決定。
all is right. (一切順利。)
all are present.(所有人都到齊了。)
2） 集體名詞作主語時，謂語的數要根據主語的意思來決定。如family, audience, crew, crowd, class, company, committee等詞後用複數形式時，意為這個集體中的各個成員，用單數時表示該個集體。
his family isn't very large.他家不是一個大家庭。
his family are music lovers. 他的家人都是音樂愛好者。
但集合名詞people, police, cattle, poultry等在任何情況下都用複數形式。
are there any police around?
3）有些名詞，如variety, number, population, proportion, majority 等有時看作單數，有時看作複數。
a number of +名詞複數+複數動詞。
the number of +名詞複數+單數動詞。
a number of books have lent out.
the majority of the students like english.