step 4
µÚËIJ½£º½«·¢ÉÒ²¿·ÖµÄ·¢Ë¿×ö¶ÔÕÛºóʹÓÃСƤ½î¹Ì¶¨£¬½«×ó²àµÄÂíβ±èÀµ½ÓÒ²à¹Ì¶¨£¬ÓÒ²àµÄÂíβ±èÀµ½×ó²à¹Ì¶¨×¡¡£
3/4