关于二度Ⅱ型房室传导阻滞的表述，不正确的是（）。

A.突然P波下传受阻，QRS波群脱落

B.下传的PR间期恒定

C.QRS波群形态大多正常，

D.听诊可发现有间歇性心搏脱漏

E.常见的病因为急性心肌梗死、病毒性心肌炎、急性风湿热等

As a result of __ is now known in physics and chemistry, scientists have been able to make important discoveries in biology and medicine.

A．it

B．what

C．which

D．that