20．I _______ the dance performance many times, each giving me a new understanding．

　　　 A．watch　　　　　　　 B．watched　　　　　 C．have watched　 D．am watching

19．The economic impact study was conducted by a group of _______ selected MBA students at the University of Kansas．

　　　 A．especially 　　　 B．specially　 　　　　 C．regularly　 　　　 D．potentially

18．_______ any other species, human populations are shaped by the usual forces of natural selection, like famine, disease or climate．

　　　 A．Compared with　 B．As with　 　　 C．As for 　　　　　　　 D．In addition to

17．- I’m terribly sorry to keep you waiting for so long．

　 - _______．

　　　 A．Never mind．　 B．That’s right．　　 C．You are welcome．　 D．Don’t mention it．

16．It’s extremely dangerous for the drivers to _______ speed as the traffic lights are changing．

　　　 A．pull up　　　　　　　 B．put up　　　　　　　 C．rise up　　　　　　　 D．pick up