Only then did he realize that he had lost a chance of achieving his dream 中为什么用did he realize
问题描述：
Only then did he realize that he had lost a chance of achieving his dream 中为什么用did he realize
答
Only提前是倒装语序 助动词也要提到主语前面
答
因为only在句首，所以要倒装。
答
Only + 状语（副词、 介词短语,从句） 放在句首时要用部分倒装,所以这么选
再如：
Only in this way 【can you learn】 English well.
答
倒装句！表示语气上的高度强调。
只有到那时，他才意识到....