b)We want to focus mainly on the action itself.

We may know who performed it, in which case we add by... to say who or what the agetn is.

-We form the third conditional with :

IF + PAST PERFECT , WOULD + PRESENT PERFECT.

-We use the third conditional to talk about the imaginary result of things that did not happen.

-We use it to express regret.

• I noticed that a window had been left open.

• Every year thousands of people are killed on our roads.

• All the cookies have been eaten.
• My car has been stolen!

• If I had worked harder at school, I would have got better grades.
• If I had had time, I would have gone to see him. But I didn't have time.
• If we had bought that house, we would have had to rebuild the kitchen.
• If we had caught the earlier train, we would have got there on time but we were late.