An Operation Analyst Is Forecasting This Year's Demand for One

An operation analyst is forecasting this year's demand for one of his company's products based on the following historical data:
$$\begin{array} { | c | c | } \hline \text { Year } & \text { \# Sald } \\\hline 4 \text { years ago } & 10,000 \\\hline 3 \text { years ago } & 12,000 \\\hline \text { 2 years ago } & 18,000 \\\hline \text { Last year } & 20,000 \\\hline\end{array}$$
What is the forecast for this year using a moving-average forecast based on the last four years?

A) 22,000
B) 20,000
C) 18,000
D) 15,000
E) 12,000