20．____ at Taiwan magician Liu Qian's magic show, many students have fallen in love with the art．

　 　　 A．Amazing　 　　　　 B．Amazed　　 　　　 C．Being amazed　 D．To amaze

19．It's becoming more and more ____ for women to keep their family name when they marry．

　 　　 A．common　　 　　　 B．ordinary　　 　　　 C．usual　　　　 　 D．normal

18．He was so deep in thought, thinking of the problem ____ he knocked into the tree without　 noticing it．

　 　　 A．when　　　 　　　 B．while　　　 　　　　 C．because　　 　　　　 D．that