A broadly defined arbitrage opportunity

a$.$ always involves buying and selling the same item.

b$.$ is relevant to the market for land, but not to other assets or factors.

c$.$ Is relevant to the market for capital, but not to other assets or factors.

d$.$ is the opportunity to buy some item $($or items$)$ at a low price and then sell in a different market for a higher price in order to earn a profit.