He kept smiling secretly and we were all wondering that made him so happy.
More highways have been built in China, __________ it much easier for people to travel from one place to another.
—Do you know the tower __________ in the heart of the city?—You mean the one __________ from the Ming Dynasty?
If we want to arrive at the village on time, we'd better __________.
Too many private cars got out and traveled __________ high speed, causing a lot of traffic accidents on the highway during the holidays.
—Are you free tomorrow afternoon?—I'm afraid not. I'll have to __________ an important lecture given by a famous professor.