Third conditional. This structure is used for unreal situations, usually because we are talking about something which happened in the past and how it could have been different. But since we can't change the past it is totally unreal or imaginary. Example:

If I had studied harder I would/could have become a doctor. 
I could/would have become a doctor if I had studied harder.

Do you understand?

If the accountants hadn't found the false entries the director

She would have passed her driving test if 

I wouldn't have been surprised if the bus _____________. But, amazingly, it was on time.

If I had bought shares in the AI company I 

wouldn't have been late for the interview.

I would have learned English quicker if I 