@ @QQQ@ @ÖïÐaínÜaì@Þî†bjnÜa@ @ .C(14,6)×C(8, 5) +C(14, 7)×C(7,5) +C(14, 7)×C(7, 4) ) 20 [PACAT] ( . . . 18 .17 ! .2 63 . 18 .18 × 2 ×17 ! = 2 ×18 ! AC B [PACAT] ( ) A .4 BB C B : B. 5 . .7