是 never have they heard,部分倒装,以下内容摘自百度百科-倒装句,想知道详细的可以查询一下
hardly,in no way,little,scarcely,seldom,never,no more,no longer,not,not only,no sooner,not only … (but also),not until… 等具有否定意义的词或词组位于句首,句子用部分倒装.
例子:
No sooner had I got home than it began to rain.
我刚到家就下起了雨.
Seldom do I go to work by bus.
我很少乘公共汽车上班.
Not until twelve o'clock did she go to bed last night .
她昨晚十二点才上床睡觉.