Management at a Particular Post Office Wants to Know About

Management at a particular post office wants to know about the quality of its face-to-face service at its customer service windows.For one week,the post office will ask the customers directly.After a customer is helped,a different employee asks the customer a short question about his or her customer service experience.The customer's comments are then transcribed by a secretary.This survey runs smoothly and a lot of customer comments are collected.What,if any,is the most noticeable bias for this survey regarding customer service at this post office for that week?

A) Nonresponse bias
B) Voluntary response bias
C) Undercoverage of the population
D) Response bias
E) There does not seem to be any bias.