“Wolf” is the singular and “wolves” is the plural.*wolf是单数形式，wolves是复数形式。

“Mouse” is the singular of “mice.”*mouse是mice的单数形式。

The verb should be in the singular.这个动词应当用单数形式。

Rewrite the sentence in the singular. [=using singular forms of words]用单数形式改写这个句子。