The police officer (who/that) I spoke to was working on the reception desk / The police officer to whom I spoke was working on the reception desk.

The things (which/that) I left on the table aren't there any more.

That's the electrician who/that did some work for my mother.

They gave us a present, which was a complete surprise

I've got two brothers, neither of whom can swim.

My girlfriend, who is an architect, is very intelligent / My girlfriend, who is very intelligent, is an architect.

The car which/that crashed into mine was a Mini.

It's too hot in my flat, which makes it impossible to sleep.

Our computer. which we only bought two months ago, keeps on crashing.

The houses, many of which were built in 1870, are still in very good condition.