Final answer:
A decrease in aggregate demand is often caused by a decrease in investment due to faltering business optimism about the future, not by expansionary fiscal policies such as increased government spending, lower taxes, or an expansion in exports.
Step-by-step explanation:
The question 'A decrease in aggregate demand may be caused by which of the following options?' relates to economic concepts, specifically those that influence changes in aggregate demand. Examining the options provided and referencing the determinants of aggregate demand, we can deduce that an increase in exports, lower personal taxes, and an expansion in government expenditures generally lead to an increase in aggregate demand. These options are usually associated with policies aimed at stimulating the economy. However, a decrease in business optimism about the future can lead to a decrease in investment, which is one of the components of aggregate demand (consumption, investment, government spending, and net exports). This could cause businesses to cut back on spending, leading to a decrease in aggregate demand.
Factors such as the decrease in foreign demand for domestic goods and the relative price increase of U.S. goods can lead to a decrease in net exports, another component of aggregate demand. Economic events and policy decisions, such as changes in consumer and business confidence, can likewise affect aggregate demand. For example, if businesses are pessimistic about the future, they may be less likely to invest in new projects, reducing the investment component of aggregate demand.
In summary, the correct option that may cause a decrease in aggregate demand is 'a decrease in business optimism about the future.' This aligns with the information presented in the various tables summarizing the determinants of aggregate demand, which indicates that changes in business confidence are significant factors affecting investment and thereby influencing overall aggregate demand.