–What made you so sad?--____________ my cellphone.
The professor you referred to in the letter______ us students three lectures by next Monday.
—What do you think has caused his heart attack? —It is ______.
—Do you have any idea why the engineer resigned? —No. In fact, everyone is ____about it.
It’s required that the students______ mobile phones in their school, so seldom ______ them using one.
“It isn’t the first time I ________ at home,” he said frankly.