英语口语之到底是什么

1) what in the world?/ what on earth? = 到底是什么？究竟是什么？
who, what, when, where, why + in the world / on earth

Who on earth would say something so mean?
What in the world are you wearing?
Where on earth are we? We are so lost !
Why in the world do you like watching "Glee"? It's so cheesy!

2) Melissa is the coolest girl on earth!
Coffee is the best thing in the world!
China is the coolest place on earth!

3) in the whole wide world （on earth 不行）
Coffee is the best thing in the whole wide world！