Which of the Following Is an Example of Assurance as a Determinant

Which of the following is an example of assurance as a determinant of service quality?

A) A doctor is highly trained in a particular specialty.
B) Employees are always visible in a hotel lobby dusting or otherwise cleaning up.
C) A college professor returns a student's call on the same day.
D) Flight attendants on a customer's regular route learn what type of beverages the customer drinks and what magazines the customer reads.