If you don’t put up the sings after school,          .

We can see only one of the doors ______.

--- How _____ hours do you sleep a day?--- Well, about eight hours. But how _____ sleep do we students really need?

Between the two roads ________ a TV tower called“Skyscraper Tower”.

Every hour and every minute ______precious to us because only six months are left for us to prepare for the college entrance examinations.