英语中名词有它的单数和复数形式，动词也有它的单数和复数形式 , 二者要一致 . 单数主语 ( subject) 名词要用动词 (verb) 的单数 (singular) 形式 , 复数主语名词要用动词的复数 (plural) 形式 . 我们写中文的不太习惯英语的这种写法 , 很难做到不假思索地配对 , 需要特别 留心才能不出错误， 特别是当主语名词和动词被分开时 . 试看下面的例句 .
A high percentage of peptides that are made of amino acids are present in the sample.
A high percentage 才是真正的主语， 而不是邻近的 amino acids , 所以应该用单数形式 .
宜改为 : A high percentage of peptides that are made of amino acids is present in the sample.
让事情更复杂的是英语名词被分为不同的种类， 其中的一类叫集合名词 . 它既可以当单数用词也可以当复数用 . 集合名词当整体 来讲时是单数，每个成员作为个体时用复数 .
The number of mice in the experiment was increased.
A number of mice have died.
All of the samples were analyzed.
All of the safety procedures was strictly followed.
代词 none 既可以是单数也可以是复数 . 当 none 后面的词是单数时 , 用单数动词 . 当 none 后面的词是复数时， 用复数动词 .
None of the information was useful.
None of the animals were starved.
描写数量， 重量，体积，时间等的词用单数， 但如果是分次添加或减少时用复数 . 在这个意义上同 集合名词类似 .
1.5 ml was added.
10 g was added .
6 hours was the required incubation time.
5 g were added stepwise.
简写的数量单位， 如 mg, ml, s 等， 单数和复数的写法是一样的 , 如 1mg, 5 mg.
一些词如 series, type, portion, class, 要用单数形式 .
A series of derivatives of penicillin was prepared.
A large portion of the reports is focused on how to deal with the increased cost.
Data, criteria, phenomena, media 是复数形式， 他们的单数形式分别是 datum, criterion, phenomenon, medium.