Emphasis (cleft sentences)

What structures (= The thing(s) that)

Puedes usar What...is/was... para enfatizar el sujeto o el objeto.

          Classical music often helps me to concentrate.
          What often helps me to concentrate is classical music.

          I don't understand where they get this stuff from.
          What I don't understand is where they get this stuff from.

It is/was... + relative clause

Esta estructura se usa para enfatizar casi cualquier parte de la oración.

          Brad Pitt married Jennifer Aniston in Los Angeles in 2000.

          It was Brad Pitt who married...
          It was Jennifer Aniston who married...
          It was Los Angeles where Brad Pitt married...
          It was in 2000 that Brad Pitt married...

A menudo se usa esta estructura cuando corriges  lo que ha dicho alguien:

          It wasn't Gwyneth Paltrow who married Brad Pitt. It was Jennifer 
          Aniston.