高频小信号放大器提出如下的指标 A: 增益（gain） B: 通频带（passband） C: 选择性（selectivity） D: 工作稳定性（stability）

Design a digital low-pass filter with a passband edge frequency of 1kHz, a stopband edge frequency of 1.5kHz and a sampling frequency of 8kHz. What are the corresponding normalized edge frequencies ωp and ωs? A: ωp=0.25π，ωs=0.375π B: ωp=0.125π，ωs=0.1875π C: ωp=0.25， ωs=0.375 D: ωp=0.125， ωs=0.1875

Design a low-pass digital filter for filtering analog signals. Its passband frequency is1.25kHz，and stopband frequency is 3.4kHz.The sampling frequency is 8kHz.The normalized cutoff frequency of the digital low-pass filter is ( ) A: ωp=2500π，ωs=6800π B: ωp=2500π，ωs=0.85π C: ωp=0.3125π，ωs=6800π D: ωp=0.3125π，ωs=0.85π