Final answer:
External factors can decrease sales for a business.
Step-by-step explanation:
External factors, such as the overall health of the economy, unemployment, or increased competition from a similar business, can decrease sales for a business.
For example, during an economic recession when unemployment rates are high, people generally have less disposable income to spend on non-essential items. This can lead to a decrease in sales for businesses.
Therefore, option b) Decrease is the correct answer.