Concept:A department store brings many different retail sections together under one roof.
Explanation:The phrase "a number of shops under one roof" means one large store that is divided into several sections.
Each section sells a different type of product, such as clothing, electronics, furniture, or home appliances.
These sections work like separate shops, but they share the same building and management.
That arrangement is the defining feature of a department store.
A discount store mainly offers lower-priced goods without such departmental division.
A chain store is a group of similar stores owned by a single company, located in different places.
A unit store usually refers to a small, independent shop dealing in a limited product line.
Therefore, the most accurate choice is a department store.
Answer:D. department store