Define the differences between abstract and concrete classes. ...

[cabate]

Define the differences between abstract and concrete classes.
 
  What will be an ideal response?

Question 2

________ specifies how the behavior of the system must be tailored to the level of its users' expertise.
 
  A) Reliability
  B) Testability
  C) Usability
  D) Maintainability

[tennis14576]

Answer to Question 1

In the hierarchy of superclasses and subclasses, some classes can be instantiated into actual (real or virtual) objects, while others cannot. Those that can be instantiated are called concrete classes; those that cannot be are abstract classes.

Answer to Question 2

C

[cabate]

Excellent

[komodo7]

Thanks for the timely response, appreciate it