複數句就是主語是複數。單數句就是主語是單數。
例如：Three apples are on the table.
單數句： An apple is on the table
複數句就是做主語和賓語的名詞，代詞都用複數表達的句子.如：
This is a book .這是單數句，因爲 this，a，book 指的都是單數.
改成複數句就是：
Thses are some e 是this 的複數 some books 是a book 的複數
There is a child.這是單數句 There are some children.
要注意因爲主語改成了複數，所以謂語動詞或be 動詞也要變化，如：
He does his homework every day.改成複數句：
They do their homework everyday.(homework 是不可數名詞，所以不變
