语法填空。阅读下面材料，在空白处填入适当内容(不多于3个单词)或括号内单词的正确形式。【辽宁卷题型】
Alan：Do you have anything__1__on this evening?
Joe：No, I've got a lot of time__2__(kill)．
Alan：Well, then. Won't you come over to dinner and have a game of Mahjong afterwards?
Joe: With pleasure.
Alan：You were not so eager about Mahjong before.
Joe：That's __3__ I didn't know the fun of__4__(play) it then. Why is Mahjong such a popular game, do you know?
