______ there was no bandage available, she tore off her sleeve and tied it around his wrist a little above    the bleeding point ______ him from losing too much blood.    [ ]

A. For; to save    

B. Because; saving    

C. Since; save    

D. As; to save

引起动作电位去极化的临界膜电位是（）

A.锋电位

B.阈电位

C.局部电位

D.动作电位

E.静息电位