The plural forms of nouns can be formed in any of the following ways:

1. Addition of -s:
Singular Plural
boy boys
girl girls
book books
pen pens
cup cups
chief chiefs

2. Addition of -es:
Singular Plural
box boxes
fox foxes
knife knives
thief thieves

3. Addition of -ies
Singular Plural
baby babies
lady ladies
lorry lorries
fly flies
city cities

4. Addition of -en
Singular Plural
ox oxen
child children

5. Some nouns change their vowels in the middle of the singular forms.
Singular Plural
foot feet
goose geese
tooth teeth
mouse mice
man men
woman women

6. There is the need to pay close attention to a small class of nouns and master them.
Singular Plural
medium media
auditorium auditoria
stadium stadia/stadiums
criterion criteria
datum data

7. However, some nouns do not change their forms, whether in the singular or plural forms.

Singular Plural
cattle cattle
deer deer
sheep sheep
news news

8. Never add s to any of the following nouns:

furniture
information
advice
equipment
stationery

8(ii).You may wish to know why. The reason is because they are collective nouns. If you want to use them in the plural forms, it is as follows:

items of furniture
pieces of information
pieces of advice
items of equipment

It is also correct to say:
some furniture/information
not
some furnitures/informations

some advice/equipment/stationery
not
some advices/equipments/stationeries

9. That said, you will also need to pay attention to words that ends in s but are not to be considered as plural nouns.

news
debris
politics
measles
economics
mathematics

For example:

Economics is my best subject.
Fake news spreads like wild fire.
Measles is a communicable disease.

10. However, there are nouns that are only in the plural forms. They can be referred to as plural only nouns. Examples include the following:

shorts
species
scissors
trousers
knickers
premises
belongings
surroundings

For example:

His shorts are dirty.
Your belongings have to be checked in.

You can check out nouns that are always in the plural forms below.

https://blog.oxforddictionaries.com/2015/05/18/12-nouns-that-are-always-plurals/

Exercise

1. Secondary schools must be equipped with.......
A. laboratory equipments
B. some laboratory equipments
C. laboratory equipment
D. many equipments

2. The........have been crying all day.
A. baby
B. babies
C. babys
D. babies'

3. Politics........meant for all the citizens, not for a few.
A. is
B. are
C. was
D. were

4. The criteria for admission into the university........made available on its website.
A. has been
B. is been
C. was
D. have been

5. While the plural form of boy is boys, the plural form of cattle is.......?



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