When working with entity relationship models $($ERM$),$ which of the following is not a valid statement regarding an entity?

a$.$ An entity is an object of interest to the end designer.

b$.$ An entity refers to the entity set and not to a single entity occurrence.

c$.$ The ERM refers to a table row as an entity instance or entity occurrence.

d$.$ In the Chen, Crow's Foot, and UML notations, an entity is represented by a rectangle that contains the entity name.