A/an, plurals – singular and plural forms

A + (#123 + 1st + N=1)

An + (#123 + 1st + N=1 + AEIOU)

Ns + (#123 + 1st + N>1)

The + (>2nd + N=1/Ns)

0 + (#123 ; =1)

A + car

An + apple, eye, idea, octopus, umbrella 

Ns + cars, apples

The + car, cars, air

0 + air

I saw a man (1st). 

The man (2nd) looked old.