Final answer:
Customer segmentation is a challenging activity in incorporating machine learning into marketing activities.
Step-by-step explanation:
One challenging activity in incorporating machine learning into marketing activities is customer segmentation. Customer segmentation involves dividing a company's customer base into specific groups based on common characteristics such as demographics, behaviors, or preferences. Determining these segments manually can be a complex task, and using machine learning algorithms to automate the process can face challenges due to the complexities and nuances involved in accurately identifying and categorizing customers.