for science

2. Nouns can be singular or plural.
When you are talking about one person,
animal, place, or thing, use a singular noun.
a ship
a woman a flower
a train
an owl

3. These are also singular nouns:
an airplane
a bicycle
a boy
a bus
a comb
a girl
a key
a letter
a map
a photographer
a refrigerator
a slide
a swing
a van

4. Use a or an before singular nouns.
Use an before words beginning with vowels
(a, e, i, o, u). For example, say:
an axe
an egg
an envelope
an ice cream
an igloo
an orange
an umbrella
an uncle
But some words don’t follow this rule. For
example, use a (not an) before these words
that begin with u:
a uniform a university

5. Use a before words beginning with the other
letters of the alphabet, called consonants. For
example, say:
a basket
a car
a hill
a house
a jar
a rainbow
a monster
a pillow
a watch
a zoo
But some words don’t follow this rule. For
example, use an (not a) before these words
that begin with h:
an heir an honor an hour

6. When you are talking about 2 or more people,
animals, places, or things, use plural nouns.
Most nouns are made plural by adding –s at the
end.
bat
bats
star
stars
mug
mugs
fan
fans
cap
caps