如图表示某种农作物品种①和②培育出⑥的几种方法，有关说法错误的是：

A．经过Ⅲ培育形成④常用的方法是花药离体培养

B．过程Ⅵ常用一定浓度的秋水仙素处理④的幼苗

C．由品种①直接形成⑤的过程必须经过基因突变

D．由品种①和②培育能稳定遗传的品种的最快途径是Ⅰ→Ⅴ

Only when he met the girl his aunt introduced to him ____ that he had seen her before.

A．he realized

B．he did realize

C．realized he

D．did he realize