低通滤波电路对信号的相移为正值，即输出信号的相位要落后于输入信号一个相角。
参考答案：对
If I ____ a bird, I would fly in the sky. [ ]
A. were
B. am
C. was
D. be
装车前应正确选择车辆，遵守货车使用限制表及有关规定。
