--- _______ can a tiger weigh, do you know? ---Yes, I know that a big one can weigh over 300 kilos. 

We know ______ about the new teacher except that she just came back from the US. We hope to know her better.

It’s ________ hard for us ________ understand what he said.

Nobody is as ______ as Sandy, so we all like to be friends with her. 

Liu Xuan is really ________,she is very good at math,  physics and chemistry.