If a series, yt, follows a random walk (with no drift), what is the optimal 1-step ahead forecast for y?10/20If a series, yt, follows a random walk (with no drift), what is the optimal 1-step ahead forecast for y?The current value of yZeroThe historical unweighted average of yAn exponentially weighted average of previous values of yGiải thíchChọn đáp án: A