Who używamy w odniesieniu do ludzi:
The girl who lives next door is very nice
who lives next door - stanowi zdanie podrzędne - relative clause
The girl - she lives nex door - is very nice.
The girl who lives next door is very nice.
I know a lot of Poles - they live in London.
I know a lot of Poles who live in London.
The man loved his car which was new.
The woman - she had a thick French accent - was very pretty.
The woman who had a thick French accent was very pretty.
That używamy w odniesieniu do rzeczy, zastępując it lub they.
Where is my pencil? It was on the table.
Where is my pencil that was on the table?
The building that I live in was built 50 years ago.
Which może być używane w stosunku do rzeczy, lecz nie do ludzi.
Where is the pencil which was on the table?