说明：  计算并划出K个长度为2的滑动平均滤波器级联后的增益响应。使用修改的程序，画出级联3个部分的滤波器的增益响应，并验证级联后的3Db截止频率。
(The gain response of K moving average filter cascaded with 2 lengths is calculated and drawn. Using the modified program, the gain response of the filter with 3 cascaded sections is drawn, and the cutoff frequency of the 3Db after the cascade is verified.)