An expert system used on a medical website accepts an input illness from the user and produces a list of possible symptoms. What type of function is the interface engine performing? A.
backward chaining
B.
production unit
C.
production rule
D.
forward chaining
E.
knowledge base

Function tipcalculate (slider, bill){  var tip = document.getelementbyid('tipamount');   var slideval = document.getelementbyid('slideval');   var bill = document.getelementbyid(bill).value;   var prcnt = slider * .01;       if (bill == null || bill == '') {      tip.innerhtml = ' enter an amount';       return false;   }  if(isnan(bill)) {      tip.innerhtml = ' enter a number';       return false;   }  if(bill > = 0){      tip.innerhtml = '$' + (bill * prcnt) .tofixed(2);   slideval.innerhtml = slider + '%';   }}