Which of the following processes is stationary? Select one: a) $y_{t}=0.2+4 t+\epsilon_{t}$ b) $y_{t}=1.2+y_{t-1}+0.8 lepsilon_{t-1}+\epsilon_{t}$ c) $y_{t}=0.7+y_{t-1}+\epsilon_{t}$ d) $y_{t}=-2+0.1 y_{t-1}-0.5 y_{t-2}+\epsilon_{t}$ SP.JG.011