------ What made you so sad?------ ______ my wallet.
— ____ sweep the classroom yesterday?—I was playing tennis with my friend.
He didn’t _____ to the news.
In the Great Depression, the American government couldn’t find good solutions _____ the unemployment problem.
In January, 2004, the United States successfully launched “Spirit”, a Mars Exploration Rover, _____ a new milestone in the history of mankind.
The speech by the mayor of Shanghai before the final EXPO 2010 is strongly impressed ____ my memory.