Plural Nouns

In English, to make a plural noun is usually to add 's' or 'es' at the end of the singular noun. For example:

a car - cars
a cow - cows
a window - windows
a PC - PCs
a tomato - tomatoes
a mosquito - mosquitoes
et cetera...

But some nouns need special care if to make their plural forms in that their plural forms don't end with 's' or 'es'.

a child - children
an ox - oxen
a mouse - mice (Beware: if it is the computer device instead of the animal: a mouse - mouses)
a louse - lice
a sheep - sheep
a man - men
a woman - women
a policeman - policemen
a foot - feet
a goose - geese
et cetera...

Some nouns of Latin, Greek and other foreign origins also take special care:

an alumnus - alumni
a radius - radii
a matrix - matrices
a château - châteaux
a fulcrum - fulcra
a cactus - cacti
a stadium - stadia
a formula - formulae
a cello - celli
a paparazzo - paparazzi
et cetera...