50．The year 2002 _____ great changes in Shanghai’s landscape.

A．sees　　　　　　　　　　 B．has seen　　　　　　　 C．saw　　　　　　　　　　 D．had seen

49．I received an invitation ____ John’s wedding, but I haven’t decided whether to accept it.

A．for　　　　　　　　　　　 B．about　　　　　　　　　 C．to　　　　　　　　　　　 D．on

48．My sister _____ the league last month and she has decided to _____ the activities to help the aged in town next week.

A．joined; join in　　　　　　　　　　　　　　　　　　　 B．took part in; attend

C．joined; involve　　　　　　　　　　　　　　　　　　 D．joined in; join in

47．– The window is dirty.

– I know. It _____ for weeks.

A．hasn’t cleaned　　　 B．didn’t clean　　　　　 C．wasn’t cleaned　　 D．hasn’t been cleaned

46．______ the temperature falling so rapidly, we couldn’t go on with the experiment.

　 　 A．With　　　　　　　　　 B．For　　　　　　　　　　 C．As　　　　　　　　　　　 D．Since

45．He ____ football regularly for many years when he was young.

A．was playing　　　　 B．played　　　　　　　　 C．has played　　　　　 D．plays

44．He accidentally ________ he had quarreled with his wife and that he hadn’t been home for a couple of weeks.

A．let out 　　　　　　　 B．took care　　　　　　 C．made sure　　　　　 D．made out