Astronomers and scientists think that a black hole is a region of space ______ which matter has fallen and _______ which nothing can escape.

es in a _____ city, I mean in a citythat is ______

Your digital camera is quite nice. Where did you buy I want to buy ， too.—On the Internet.

Why do you like climbing mountains –Because they are there and climbing is _____thing Ihave ever done.

Alice, how do your parents like pop music–____ my dad my mum likes it. But they both prefer Beijing Opera.