The building used by the professional is called _________ office.

The correct answer is: A. Quiet

An office is a building or room where people work, especially in a professional or administrative job. It is usually a quiet place where people can concentrate on their work.

The other options are incorrect because:

• B. Sound is not a word that is typically used to describe an office.
• C. Big and D. Small are not relevant to the question of what type of building is used by professionals.