19. If you are not sure _______ your strengths and weaknesses ______, you may ______ a professional expert so that you can develop yourself to the full.
— I put him down for a well-educated man. —______ ? — I mean that he's a well-educated man.
The silence of the library is sometimes broken by a sudden cough or the sound of pages______.
Wang Pin is an advanced worker in our company. He _______ for four years in Yangzhou University.
When it______ air pollution, Beijing faces the three “C” s-----cars,coal and construction,which lead to Beijing's thick air pollution.
______ it have been the failure to pick up directions from the ground control that caused the air crash?