Irregular plural Nouns: Base plural and Irregular endings

https://liuxue.ef.com.cn/english-references/english-grammar/singular-and-plural-nouns/

End -f to -ves

Word end with "f", change "f" to "ves".

For instance：

leaf ---> leaves（叶子）

loaf ---> loaves（面包）

calf ---> calves（小牛）

End add -en

Only four irregular plural nouns will end in "en".

They are：

Child ---> Children（小孩们）

Ox ---> Oxen（公牛们）

Brother ---> Brotheren

Sister ---> Sisteren

Among them, only "Children" is often used.

Base Plural(Plural is the same as Singual)

Sheep

Fish（如果是指 fish 的种类，则为 fishes）

Deer（鹿）

Species（物种）

Aircraft（飞机）

For instance：

There was one sheep on the hill.

There were two sheep on the hill.