Explanation

An article is any member of a class of dedicated words that are used with noun phrases to mark the identifiability of the referents of the noun phrases. 

Explanation

The definite article (the) is used before a noun to indicate that the identity of the noun is known to the reader

Explanation

An apple a day keeps the doctor away is the correct sentence.

The article "An" is used before words starting with a vowel sound.

Explanation

Cooperative learning is form of constructivism

Explanation

Article (a,an,the) are used before a noun.

Explanation

Here boy is not specific.

We use the for specific nouns.

A boy is swimming in the pool. (Correct)

Explanation

It is only after a war is over the people realise how bad it was.

Explanation

Articles "A" and "AN" are used with some expressions.

For example:

Make a noise, give a warning, have a pain, have a great education etc.

Explanation

"An" is used before words that start with a vowel sound.

"She did not have an apple".

اس کے پاس سیب نہیں تھا۔

Explanation