Everyone knows _____ is dangerous to play with fire, but _____ is difficult is to prevent children from

playing with fire.   [ ]

A. that; it      

B. it; it      

C. that; what      

D. it; what

下列证据中，证明力最强的是( )。

A．关于应收账款的函证回函

B．询问独立第三者的书面答复

C．被审计单位开具的销货发票

D．严密的内部控制下形成的会计记录