题目

Either the boy or his sister must have   dinner here. A. his   B. her  C. their   D. theirs 答案：C 如图，AB、CD分别为两圆的弦，AC、BD为两圆的公切线且相交于P点．若PC＝2，CD＝3，DB＝6，则△PAB的周长为何？ [　　] A．6 B．9 C．12 D．14