_____ was known to all, John had broken his promise _____ he would stay with us for some

time. [ ]

A. As; that

B. As; which

C. It; that

D. Which; that

从传导速度来看，有髓的神经纤维较无髓的（）。

A.传导更远

B.传导更快

C.传导更慢

D.传导更近