Count nouns are people, places or things that we can count individually (one by one). 

Count nouns can be singular or plural.

Expressions with one of the,  every, and each before the noun take a singular verb. (Every country has a capital.)

Ecpressoins with a few of the, some of the, many of the, all of the etc, take a plural verb. (All of the cities have capitol buildings.)

A forest

Rivers

A mountain range

Every national park

Many of the people

Each of the farms

All of the states

Every state

Several of the countries

one of the cities

Some of the kids

A few of the students ___ in the classroom.

Every car ___ parked outside.

Some of the apples ___ rotten.

Every student ___ ready for the test.

All of the boxes ___ still unpacked.

One of the books ___ new.

A few of the lights ___ in the basement.

Every tree ___ tall and healthy.

All of the dogs ___ barking.

There ___ a cup of coffee on the table.