1£®ÒÑ֪ȫ¼¯ ,¼¯ºÏ ,Ôò Ϊ£¨ £©
A£® B£® C£® D£®
2£®º¯Êý µÄ¶¨ÒåÓòΪ£¨ £©
A£®[1£¬2£©∪£¨2£¬+∞£© B£®£¨1£¬+∞£©
C£®[1£¬2£© D£®[1£¬+∞£©
3£®ÈôÖ¸Êýº¯Êý ÔÚ ÉÏÊÇÔöº¯Êý, ÔòʵÊý µÄÈ¡Öµ·¶Î§ÊÇ£¨ £©
A£® B£® C£® D£®