20．No one can walk the wire without a bit of fear unless ________ very young.

A. having been training　　　　　 B. trained　　　 C. to be trained　　 D. being trained

19．_________ the cold weather, the volunteers came to clean the street as usual.

　　　 A. Besides　　　　　　　　　　 B. Even though　　　　　　 C. Although　　 　 D. Regardless of

18．---Did you learn to drive 10 years ago?

　　 ---Yeah, I am sure he _________ for at least 10 years.

　　　 A. had driven　 B. has been driven　 C. has been driving 　　　 D. has driven