仲有個問題(20分)
http://hk.knowledge.yahoo.com/question/question?qid=7009020701722
更新1:
20分 問題 http://hk.knowledge.yahoo.com/question/question?qid=7009020701951
更新2:
20分 http://hk.knowledge.yahoo.com/question/question?qid=7009020702537