Answer:
Option A
Step-by-step explanation:
A biased sample is the one in which only that part of a lot is chosen as sample which works with the decision desired. As for in the given case, the store chooses to receive a review from the customers who are happy.
A smiling face confirms that the person is happy with the store service.
Thus, when we provide them the comment card maximum feasibility is that they shall write back a positive comment about the store service.
In this manner if comment card is not provided to unhappy customers, the opinion formed is a biased opinion.
Final Answer
Only customers with happy faces are given an option to fill the comment card.