There are a few nouns in English that are irregular and as a result, the plural form does not use an "s". Look at the following words - do you know how you would change the singular form to the plural form (remember that these are irregular so adding "s" doesn't work, and some of them will remain the exact same in plural form).
Person / Man / Woman / Child / Tooth / Foot / Knife / Life / Wife / Cactus / Mouse / Goose / Wolf / Moose / Deer / Sheep / Fish / Shrimp / Octopus
You can find the plural forms for each below:
Person = People
Man = Men
Woman = Women
Child = Children
Tooth = Teeth
Foot = Feet
Cactus = Cacti
Mouse = Mice
Goose = Geese
Wolf = Wolves
Moose = Moose
Deer = Deer
Sheep = Sheep
Fish = Fish
Shrimp = Shrimp
Octopus = Octopi
Practice
Change the underlined word into plural form. Try to not look at the answers above and then find out if you were correct.
I can’t eat a shrimp. I’m allergic to seafood.
I saw a mouse in my garage.
There is a fish in the pond.
She has a child.
A man doesn't have to experience pregnancy like a woman does
I wore braces in high school so that my tooth would be straight.
My foot hurt from walking all day.
I was disappointed because I didn't see a wolf at the zoo.
Wool comes from a sheep
A person who sleeps 8 hours a night are usually much healthier than a person who sleeps only 5 hours a night.
All of the my friends came with their wife
The soldiers risked their life to fight in the war.
Answers
I can’t eat shrimp. I’m allergic to seafood.
I saw mice in my garage.
There are fish in the pond.
She has children.
Men don't have to experience pregnancy like women do.
I wore braces in high school so that my teeth would be straight.
My feet hurt from walking all day.
I was disappointed because I didn't see wolves at the zoo.
Wool comes from sheep.
People who sleep 8 hours a night are usually much healthier than people who sleep only 5 hours a night.
All of the my friends came with their wives.
The soldiers risked their lives to fight in the war.