请教此英文句子的语法结构.

这里用的是部分倒装的结构。当never,hardly,seldom,little,few,not until,not,no,no sooner,by no means,under no circumstances等否定词置于句首时,其后要用部分倒装。如：Never did I see him again。后来我再也没见到过他了。Little did I dream that the girl was my niece。我做梦也没想到那女孩是我的侄女。后面的句子用部分倒装,即将主语与助动词倒置,其结构与一般疑问句大致相同little不是主语。主语还是they,they know little when……是正常的语序。that是引导定语从句