Final answer:
Buying and selling products are considered operating activities, which are part of the day-to-day operations of a business to generate revenue.
Step-by-step explanation:
Buying and selling products are examples of operating activities. Operating activities are the day-to-day actions that companies engage in to run their business and generate revenue, such as selling products or services and buying supplies or inventory. These are distinct from investing activities, which involve the purchase or sale of long-term assets like machinery and buildings, and financing activities, which include actions like raising capital through issuing stocks or taking on debt. Therefore, the correct answer to the student's question is 'a. Operating activities'.