Jack's speech was heard by a group of five judges,all of ____ agreed that it was the best one thisyear. [ ]

A. who      

B. which    

C. that      

D. whom

变压器瓦斯保护动作原因是由于变压器（）。

A.内部故障

B.套管故障

C.电压过高

D.一、二次侧之间电流互感器故障