In the long run, if velocity is constant, then ______ determines real GDP and ______ determines nominal GDP.

In the long run, real GDP is determined by the productive capacity of the economy, also known as potential GDP. This is influenced by factors such as technology, resources, and labor force participation, rather than monetary factors. If velocity is held constant, it implies that the rate at which money circulates in the economy doesn't change, reinforcing the idea that the real output is strictly a function of the economy's capacity.

On the other hand, nominal GDP is influenced by the money supply. Nominal GDP reflects the total dollar value of all goods and services produced in an economy, measured at current prices. If the money supply increases, and assuming velocity remains constant, nominal GDP would also tend to increase due to higher prices.

Thus, the correct relationship is that the productive capability of the economy determines real GDP, while the money supply determines nominal GDP, making this answer the most accurate representation of the long-run relationships in macroeconomic theory.