Which of the following is an AR(3) model?
a) yt = 8 + 01yt-1+02yt-2 +03yt-3 + 80X + 81Xt-1+ 82Xt-2+ 83Xt-3 + Vt
b) yt = 8 + 01yYt-1+ 80X + 81Xt-1+ 82Xt-2+ 83Xt-3 + Vt
c) yt = 8 + 01yt-1+02Yt-2 +03yt-3 + 80X + 81Xt-1+ Vt
d) yt = 8 + 01yt-1+02Yt-2 +03Yt-3 + Vt