If we want to give particular importance to a person, a thing or a clause in a sentence, we can use these structures:
1. It is/was...that can be used:
- with (only) when, while or not until to emphasize a (period of) time
It was only when I got home that I realized someone had stolen my wallet.
It was while he was in Spain that Lennon wrote "Strawberry Fields Forever".
It wasn't until he took off his hat that I recognized him
- with because to emphasize reasons
Perhaps it's because I'm a chef that people never invite me to their dinner parties.
- to emphasize prepositional phrases
It was on the radio that I first heard the news.
It was in France, not their native England, that they first became famous.
- to emphasize a thing or a person
"who" can be used instead of "that" if we are referring to a person.
It was Gary that/who broke the chair.
It's his left arm that's broken, not his right one.
Modal verbs can be used instead of is/was
It can't be my mobile phone that's ringing- it's switched off.
It might have been the fish that made me feel ill.
2. What...is/was can be used to emphasize:
- a noun
What I most wanted to see in the Louvre was the Mona Lisa.
What I need is a cup of strong, black coffee.
- an action or series of actions
What you do then is (to) add the flour and stir it in thoroughly.
What happened was (that) I left my wallet in the café and had to go back.
I couldn't find my key, so what I did was (to) try and climb in through the window, but what happened was (that) a passer-by saw me and phoned the police.
All can be used instead of What to mean "the only thing that".
All he (ever) did during the school holidays was (to) play on his computer.
All I really want is a little house in the countryside.
Don't make a fuss. All I did was (to) spill some milk.
He's so boring. All he (ever) talks about is football.
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