The subject must agree with the verb in number and person. Basic rules of sentence agreement are given here.
The indefinite article (a/an) is used before a noun in the following cases:
a) To convey the numerical sense of one
I have a pen.
There is a cat on the roof.
A hundred kilos make a quintal.
Kinds of Sentences
A simple sentence consists of a single main clause.
She wrote a letter.
They visited us yesterday.
It is snowing.
We have been waiting for hours.
Good books build character.
Birds of a feather flock together.
A sentence is the largest grammatical unit in any language. In English, a sentence always contains a subject and a predicate.
A sentence is a group of words arranged in a specific order which makes complete sense.
There are different kinds of sentences and they are