20．___ abstract, Galileo's theory was quite difficult to understand of his time．

　 　　 A．Sounding　　　　　　　　　 　　　　　　 B．Sounded

　　　 C．To sound　　　　　　　　　 　　　　　 D．Having been sounded

19．-Was his father very strict with him when he was at school?

　 　-Yes．He had never praised him ____ he became one of the top students in his grade．

　 　　 A．after　 　　　　　　　　 B．unless　　 　　　　　 C．until　　　　　 　 D．when

18．-I'd like to find a part-time job in the restaurant．

-Good idea. In my opinion, ____ it doesn't affect your studies．

　 　　 A．unless　 　　　　　　 B．more that 　　　　　 C．even if　　 　　　　 D．as long as

17．Many little children suffer from kidney stone and the disease is reported ____

　　 by the milk powder they eat．

　 　　 A．to cause　　　 　 　　　　　　　　　　　　　　　　 B．to be caused　　　 　　　　　　　　　　　

　　　 C．causing　　　 　　 　　　　　　　　　　　　　　　　 D．being caused

16．She doesn't like Miss Anderson, so she always avoids ____ with her．

　 　　 A．being leaving alone　　　　 　　　　　　　 B．being left alone

　 　　 C．being leaving behind　　　　　 　　　　　 D．being left behind