The answer is Sarima (0,0,1) * (1,0,0)12. Can you please briefly explain how is that?

Solution: The ACF is decreasing at multiples of 12 . So a seasonal AR(1) component with S=12. Also, within a period, only the first lag is non-zero, so another MA(1) component. So the simplest model with this pattern is an SARIMA(0,0,1)(1,0,0)12 model