Lo o Lo que...

What you said to Checho was not true!

The worst is not sleeping when you are sick.

That is the most interesting thing I've heard in years.

It is a mystery what you want to do with that. (misterio)

The best thing about my city is that it is friendly. (amigable)

A house full of dogs is what I want!

This office has everything that we need.

The new thing is not always the best thing.

What I like about the movie is that it has a happy ending. (un final/an ending)

We want the best for them. (Everyone is masculine.)