Nobody believed his reason for being absent form the class  _____ he had to meet his uncle at the air port. 　　[ ]

A. why

B. that　　

C. where

D. because

有两个开关量输入信号Z1和Z2，通过异或运算后的输出信号Q，若其中输入信号Z1、Z2都为1，则输出信号Q为（）。

A.0；

B.1；

C.2；

D.不确定。