有四个不同的正整数a，b，c，d，若a²+2cd+b²，c²+2ab+d²的值都是完全平方数，且a+b+c+d的值最小，则a，b，c，d的值从小到大分别为______．

Only when they were told the date of the wedding ,____ their daughter would get married.

A．realized they

B．did they realized

C．did they realize

D．they did realize