'child' 的复数是 'children'。

"Children" is the ___plural of "child."

'tooth' 的复数形式是 'teeth'。

The ___plural form of "tooth" is "teeth."

要构成复数，你通常在一个词的末尾加 -s。

To form the ___plural, you usually add -s to the end of a word.