Answer:
A) is the most visible part of the firm.
Explanation:
The importance of service employees is that they are the ones that actually deal with the company's customers. If service employees don't deal properly with the clients, then no matter how good the company's products are, the customers will not be satisfied or happy.
For example, if the waiter in a restaurant is rude with the customers, the whole dining experience will be ruined and the customers will consider the restaurant's service as bad even if the food served was great.