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Consider a four-point moving average filter defined by the equation $y[n] = \displaystyle{}\sum _{i=0}^{3}\alpha_{i}\:x[n-i].$ The condition on the filter coefficients that results in a null at zero frequency is

- $\alpha_{1} = \alpha_{2} = 0;\:\alpha_{0} = -\alpha_{3}$
- $\alpha_{1} = \alpha_{2} = 1;\:\alpha_{0} = -\alpha_{3}$
- $\alpha_{0} = \alpha_{3} = 0;\:\alpha_{1} = \alpha_{2}$
- $\alpha_{1} = \alpha_{2} = 0;\:\alpha_{0} = \alpha_{3}$