下列有关汇款人申请退汇的描述不正确的是（）
A.3日以内
B.3个工作日以内
C.当日
参考答案：C
已知三点P（1，2），Q（2，1），R（3，2），过原点作一直线，使得点P，Q，R到此直线的距离的平方和最小，求此直线方程．
Not until they left school ______ how much their teachers loved them and helped them. [ ]
A. they realized
B. had they realized
C. they would realize
D. did they realize
