Futures implement a margin mechanism, trading the standard contract of the commodity rather than the commodity itself. Therefore, only a certain margin is needed in futures, and goods can be bought and sold directly as needed. Short selling is the operation of selling commodity contracts directly when the expected commodity prices fall. Because it is a commodity contract to be delivered at a specific time in the future, you only need to fulfill the contract before the expiration date, and you don't need to have a corresponding contract when you sell it. Means of performance are divided into hedging and delivery. Hedging refers to buying equal contracts to close positions, and delivery refers to taking out qualified physical objects.