Final answer:
In the dynamic AD-AS model, the central bank's primary policy instrument is the money supply. The central bank can control the money supply through open market operations.
Step-by-step explanation:
In the dynamic AD-AS model, the central bank's primary policy instrument is the money supply (option a). The central bank can control the money supply by buying or selling government bonds in open market operations, which affects the amount of money available in the economy. By increasing the money supply, the central bank can stimulate economic growth, while reducing the money supply can help combat inflation.