. The reason for all the changes being made _______to us yet.

A．has not explained

B．has not been explained

C．did not explained

D．were not explained

急性化脓性中耳炎的病理改变包括（）

A.鼓室内血浆、纤维蛋白、红细胞及多形核白细胞渗出

B.鼓室黏膜增厚，纤毛脱落，杯状细胞增多

C.鼓室内有炎性渗出物聚集，并逐渐变为脓性

D.鼓室内压力随鼓室积脓增多而增加，鼓膜受压而贫血，且因血栓性静脉炎终致鼓膜穿孔

E.以上均正确