Since the trader has a short position in wheat futures, they will want the price of wheat to decrease. With a short position, the trader profits if the price of the asset decreases.
And for a trader who has a long position in wheat futures, they will want the price of wheat to increase. With a long position, the trader profits if the price of the asset increases.
Therefore, the correct options are:
a) decrease, increase
A trader with a short position wants the price to decrease, while a trader with a long position wants the price to increase.