Final answer:
A decrease in the current price of a substitute product will decrease the current demand for the original product as consumers will choose the more affordable option.
Step-by-step explanation:
Among the given options, the factor that will decrease the current demand for a product is option B: "A decrease in the current price of a substitute product." This occurs because consumers are likely to choose the more affordable substitute product over the original product, leading to a decrease in demand for the latter. Other factors that can also cause a decrease in demand include lower consumer income levels, expected substantial price increases for the product, or a reduction in the number of buyers.
Conversely, a higher price for a complementary good can shift the demand curve for that good to the left, impacting the original product. Additionally, changes in expectations about future prices can influence current demand, as consumers may increase demand now to avoid anticipated higher prices later. These dynamics highlight the complex interplay of factors that affect the demand for a product in the market.