Not until he left his home _____ to know how important the family was for him.

A．did he begin

B．had he begun

C．that he began

D．he had begun

篇段积累——默写韩愈的《马说》选段。

　　世有伯乐，然后有千里马。千里马常有，而伯乐不常有。故虽有名马，                                    ，                                        ，不以千里称也。