183. --- You look pale, what troubled you?

--- I ______ my dead friend.

A．am thinking about

B．was thinking about

C．had thought about

D．will think about

表明失误链形成的主要迹象有（）。I.不确定性；II.注意力分散；III.感知不全面或混乱；IV.通信中断。

A.I+II+III

B.II+III+IV

C.I+II+IV

D.I+II+III+IV