19. --- Could you tell me how the sea sand comes about ? --- Sea waves dash against the rock. In this way , the sea sand ___ .
Parents have a duty to ____ their children from the harmful effects of the Internet.
Qiandao Lake, widely known ______ a tourist site, is famous _____ its clear and drinkable water.
We have every reason to believe that __________ 2012 London Olympics will be ________ great success.
—Madam, could you please tell me how to get to the nearest post office? —_______
Entering the room, I found Mary ______at the desk and ______a letter.