estimated using ordinary least squares

estimated using ordinary least squares?
(i)An AR(1)
(ii)An ARMA(2,0)
(iii)An MA(1)
(iv)An ARMA(1,1)

(i) only
(i) and (ii) only
(i), (ii), and (iii) only
(i), (ii), (iii), and (iv)
Consider the following AR(2) model. What is the optimal 2-step ahead forecast for y if all information available is up to and including time t, if the values of y at time t, t-1 and t-2 are –0.3, 0.4 and –0.1 respectively, and the value of u at time t-1 is 0.3?
 -0.1 0.27 -0.34 0.30
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