微生物鉴定系统编码的工作原理是将生化反应的阴阳性结果转化为（）

A.数字信号

B.模拟信号

C.脉冲信号

D.点阵信号

E.激光信号

I ________ my homework while my parents ________ TV at 9 last night.

A．did; have watched

B．had done; were watching

C．was doing; were watching

D．would do; were watching