Answer:
c. Observation.
Explanation:
If a company wants to gather information about it customer's decision making criteria, the best method is Observation. It allows researchers to gather large data in natural situations.
Focus group will only give analysis of selected group. This is usually beneficial before the launch of a product.
Emails and Mails survey have drawbacks like customers may ignore, might not receive mails, doesn't respond on time.
Personal interviews can be time consuming and customer might not be comfortable about explaining their product selection criteria.
