ans will be B
The User Interface - Where the user interacts with the expert system. In other words where questions are asked, and advice is produced
The inference engine is the main processing element of the expert system. The inference engine chooses rules from the agenda to fire. If there are no rules on the agenda, the inference engine must obtain information from the user in order to add more rules to the agenda
The Knowledge Base - Where the information is stored in the expert system in the form of facts and rules (basically a series of IF statements). This is where the programmer writes the code for the expert system.
Explanation module . Gives the user, the ability to follow inferencing steps at any time during consultation