Because you can see right through them!
or
The library, because it has the most stories.
or
No, but hum a few bars and I'll fake it.
or
Two, one to screw it in, and another to repent.
or
Because it's two tired!
or
He was trying to fetch a boomerang
or
Leap Year
or
The ceremony was rubbish - but the reception was brilliant.
or
Tyrannosaurus wrecks.
or