Originally posted by ndmmxiaomayi:
You need the English as it is Broken book.

Actually, this wouldn't be of much help as it needs you to understand some basic knowledge. I suggest you get some primary school grammar books to do. Read, understand and practise. I like those tiny thick books by Cosco, not too sure if it's still in production.
The
girl fails her exam.
The
girls fail their exams.
And this is wrong.
Correct one should be: The
girl fails her exams.
Although exams is plural, it's not the subject of the sentence, thus it wouldn't affect the verb.
And remember what's a verb. It's an action word. Exams is not doing anything, thus it wouldn't even qualify.
The part to read up and practise on is Subject-verb agreement.
Sentences basically are made up of one or more "clauses"
Its hard to explain what a clause is, but I hope the example below gives you an idea:
I ate the cake ( 1 clause )
I ate the cake and drank milo ( 2 clauses )
In each clause there must be at least one noun (or noun group) and one verb (or verb group)
Nouns, very simply put are words that refer to people, places etc. It actually goes further than that. Words that can be treated as objects are also classified as nouns (Abstract Nouns, I think.... heard another name for it but cannot remember it now) For example:
His
stupidity never fails to amuse me.
His
recklessness gets him into a lot of trouble.
In the example you see the words "stupidity" and "recklessness" used as nouns like how I would say, "His pencil" or "His pen"
The center of any sentence is its Verb or Verb group.
The Verb simply put is "An action word"
Thus words like "eat", "sleep" are all verbs.
This Verb has at least one or more of the following that's related to it.
The Subject and the Object. The Subject can be seen as the person doing the action. The Object... is the person/thing the action is done on. The Object of the action. For example.
The SAF soldier smuggled a gun out of camp.
S + V + O
subject = SAF soldier
Verb = smuggled
object = a gun
SVO is the most basic of sentence structure and is called an active sentence.
The Gun was smuggled by the SAF soldier
O + V + S
Even though the order of the words are changed, the gun is still the object of the action. And the SAF soldier is still the person doing the action.
Sentences of this structure are called passive sentences.
What Subject-Verb Agreement says is that,
For each clause, the subject must agree with the verb. Note that this is true for each clause in the sentence. So you can have more than one clauses, and each clause may be singular or plural.
For example.
He shoots the pigs while they shoot the monkeys.
First Clause : He shoots the pig (S = He (singular) V = shoots (singular) O = pigs (plural))
In this clause, you notice that the Verb only needs to agree with the subject. Yes, most singular verb has a "s" after the root verb.
Second Clause : They Shoot the Monkeys (S = They (plural) V = shoot (plural))
There, long-winded but I hope informative.