The input and output of a continuous time system are respectively denoted by x (t) and y (t). Which of the following descriptions corresponds to a causal system ?
|(A) y(t) = x(t ? 2) + x(t + 4)||(B) y(t) = (t ? 4) x(t + 1)|
|(C) y(t) = (t + 4) x(t ? 1)||(D) y(t) = (t + 5) x(t + 5)|
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