主谓一致

*单数*：She has a cat.

*复数*：They have cats.

名词复数

*单数*：There is a book on the shelf.

*复数*：There are books on the shelf.

指示代词变化

*单数*：This is my friend.

*复数*：These are my friends.

疑问句转换

*单数疑问句*：Is this your phone？

*复数疑问句*：Are these your phones？

不定冠词调整

*单数*：He is a student.

*复数*：They are students.

补充说明

复数形式需同时修改主语、谓语和名词（如a→复数名词、is→are）；

不可数名词（如information）无需变为复数；

专有名词（如China）单复数同形。通过以上例句，可系统掌握英语中单数与复数的转换规则。