Countable nouns

Pluralize them:
Cars are essential means of today’s transportation.
Nurses are more likely to retire sooner than doctors.

Uncountable nouns

Just use the simple form of the word:

Water is found almost everywhere on the planet.
Coffee grows in hot places.

Note: uncountable nouns act like a singular countable noun, so the verb “is” fits here.

Note: Do not use definite article “the” as the meaning will change.
[The] customers are always right.

Special words:

Everyone enjoys listening to music.
No one can tolerate harsh weather conditions in Antarctica.
Nobody has ever set foot on Mars.

Note: These words act like a singular countable noun.

Special adverbs:

Generally, you cannot get a good job without enough education.
In general, women tend to talk about their feelings more than men.
By and large, charities do not pay federal tax.

Note: Use a comma after all these adverbs.

Adjectives

Yes! You can generalize using adjectives. Follow this formula:

the + adjective

Take a look at these examples:

The rich are getting richer and the poor are getting poorer.
Out with the old, in with the new
People should help the desperate and the destitute.

Note 1: Use this structure only about well-known groups of people.
Note 2: This structure acts like a plural countable noun.

Singular nouns

Yet another surprise: singular nouns can be used to generalize too:

the + singular countable noun

Here are some examples:

The wheel has revolutionized human transportation.
The horse is an elegant animal. (the horse = horses)
Schools should concentrate more on the child and less on exams.
The city can be intolerable for migrants, especially the unskilled.

Note 1: This structure is common for the names of scientific instruments and inventions, and musical instruments..
Note 2: This structure acts exactly like a singular countable noun.

Answer Key:

a) University is a place to study. (This is not general. It defines the word “university”.)
b) Universities are places to study. (This means universities in general.)
c) The university is a place to study. (This means universities in general.)
d) A university is a place to study. (This means any university [out of many] can be a place to learn something.)

The correct answers are B and C.