There are four types of conditional sentences in English: zero conditional, first conditional, second conditional, and third conditional. The zero conditional refers to general truths using the present tense. The first conditional expresses possible future events using "if + present, will/can/may + future". The second conditional discusses unlikely events using "if + past, would/could/might". The third conditional refers to unreal past events using "if + past perfect, would/could/might have".

1. Conditional Sentences
There are four main types of if sentences in English, often called conditional
sentences.
These sentences are in two halves, with the if part in one half and the other part
where you can use modal verbs such as can, will, may, might, could and would.
The Zero Conditional – “If + present form + present form”
“If you heat ice, it melts.”
In this type of conditional sentence, you could use when instead of if. It’s always
true that when you heat ice it melts. This is why this type of sentence is
sometimes called a zero conditional.
The First Conditional – “If + present form, + will, can or may”
“If I am late, I will call you.”
“If you need me, you can call me at home.”
“If it gets any hotter, we may have a thunder storm.”
In these sentences (or first conditional sentences), there is a strong possibility
that the first part (coming after if) is going to happen. The second part says what
will happen as a result.
The Second Conditional – “If + past form + would, could or might”
“If I got a pay rise, I would buy a new car.”
“If you left your job, you could travel around the world.”
“If you were nicer to him, he might lend you the money.”
In these sentences, the first part with if shows that the event is unlikely to
happen. In English, we often use this type of sentence (called a second
conditional) to talk about hypotheses, or imaginary future events.
For example, “If I was President of the United States, I would change some
laws.” But I know that I’ll never be the President of the USA – I’m just saying
what I would do if I was in his/her position. Note: in American English, it is
correct to use “if I were…” In British English, it’s more common to say “if
I was…”

2. The Third Conditional – “If + past perfect + would/might/could have done”
“If I had revised, I would have passed my exams.”
“If we had gone out earlier, we might have got to the cinema on time.”
“If you had told me there was a problem, I could have helped.”
In these sentences (called “third conditional sentences”), the first part of the sentence
with if didn’t happen. So there is no possibility of the second part of the sentence
happening. I didn’t revise, so I didn’t pass my exams and there is nothing I can do about
it now. English speakers use this type of sentence to show how things could have been
different.
Choose the appropriate options to complete the sentences.
1. Many people who live near nuclear plants are concerned. ---- go wrong, the
impact on the surrounding area could be disastrous.
Something would
Something will
Should something
Does something
2. Had I known the carpenter was going to take three days to show up, I ---- the
materials and done the work myself. It would have been finished by now.
will get
would have gotten
might get
will have gotten
3. I wish you ---- making that noise. It's bothering me.
would stop
are going to stop
stop
can stop
4. If I can speak Spanish, I ---- next year studying in Mexico.
would spend
would have spent
had spent
will spend

3. 5. It would have been a much more serious accident ---- fast at the time .
had she been driving
was she driving
she had driven
she drove
6. "Can I borrow your car for this evening?"
"Sure, but Nora's using it right now. If she ---- it back in time, you're welcome to
borrow it."
brought
would bring
had brought
brings
7. We ---- the game if we'd had a few more minutes.
might have won
won
had won
will win
8. If you ---- to my advice in the first place, you wouldn't be in this mess right
now.
listen
will listen
had listened
listened
9. If I ---- the same problems you had as a child, I might not have succeeded in
life as well as you have.
have
would have
had had
should have
10. ---- more help, I could call my neighbor.
Needed
Should I need
I have needed
I should need