--- What would you like, sir? --- ______.

Scientists are hoping for a _____ in the search for a cure for cancer. 

Scientists have found no ________of life on Mars so far,though great efforts have made on the research.

The _______ that the injured be sent to the hospital without delay turned out to be wise.

—I am afraid this pair of shoes is a little expensive．—If you really want to buy them, I will give you a ____ of 10 percent．