Good friends __________ we are, I still find her difficult to understand at times.  [ ]

A. as

B. because  

C. though

D. unless

复式记账凭证的优点有( )。

A．能全面反映账户的对应关系

B．有利于检查会计分录的正确性

C．便于分工记账

D．便于按会计科目进行汇总