Theorie:

Relative clauses. Clauses with who/that/which. Part 2
 
You must use who/that/which when you refer to the subject of the relative clause.
 
Sometimes who/that/which is the object.
 
Have you found the keys that you lost?
  
7618827242_efd89e2a8f_b.jpg

1. When who/that/which is the object, you can drop it.

The woman I wanted to see was away.

The dress Kate bought doesn’t fit her very well.
 
 
2. Note the position of prepositions (in/to/for) in relative clauses:

Are these the books you were looking for?

The woman he fell in love with left him after a month.
 
скачанные файлы.jpg
 
3. You cannot use what in the following sentences:

Everything (that) they said was true.

I gave her all the money (that) I had.

What = ‘the thing(s) that’.

Did you hear what he said? (= the things that he said)
Quellen:
www.flickr.com
whytoread.com