a or an
a or an
a or an
a or an
a or an
100

egg

an egg

100

box

a box

100

rat

a rat

100

dog

a dog

100

school

a school

200

orange

an orange

200

cat

a cat

200

teacher 

a teacher

200

elephant

an elephant

200

ox

an ox

300

girl

a girl

300

robot

a robot

300

apple

an apple

300

arm

an arm

300

ant

an ant

400

fish

a fish

400

CD

a CD

400

book

a book

400

notebook

a notebook

400

ear

an ear

500

umbrella

an umbrella

500

fox

a fox

500

table

a table

500

tree

a tree

500

chair

a chair