To use Java built-in sorting method Collections.sort(aList, aComparator): (Check all that apply.) aComparator is an object of class which implements Comparator a compiler error will occur if aComparator is missing. aComparator is necessary if the item in aList doesn't implement the Comparable interface. aComparator is not needed if the item in aList is a Java built-in type like String. aComparator is always needed