Final answer:
The health insurance call center associate should first say option b, 'I'm sorry. It must be very frustrating that this is not resolved yet?' to show empathy towards the upset customer.
Step-by-step explanation:
In this situation, it is important for the health insurance call center associate to handle the upset customer with empathy and understanding. The representative should first say option b, 'I'm sorry. It must be very frustrating that this is not resolved yet?' This response acknowledges the customer's feelings and shows empathy towards their situation. By validating the customer's emotions, the representative can work towards finding a resolution.