An off-the-shelf software package that implements an inference engine,
a mechanism for entering knowledge, a user interface, and a system to
provide explanations of the reasoning used to generate a solution is
called:

A.
A knowledge base

B.
A knowledge acquisition system

C.
An expert system shell

D.
A neural network

Explanation:
An expert system shell provides the fundamental building blocks of
an expert system and supports the entering of domain knowledge.
Thus, for an application that is not complex and does not require the
custom development of the components of an expert system, an
expert system shell is a useful tool that will save development time.
*A knowledge base is a component of an expert system.
*. A neural network is another type of artificial
intelligence system that uses the neurons of the brain as a model and
solves problems using nonlinear pattern-matching techniques and
learning approaches.
*A knowledge acquisition system refers to the means of identifying and acquiring the knowledge to
be entered into the knowledge base. In simple terms, it is trying to determine how an expert thinks
when developing a solution to a problem.