Which are true about instance variables of a class (check all that apply): Group of answer choices They should usually be declared private. Member instance methods of the same class must use this. before their names in order to access them. Member instance methods of the same class must use mutator methods to modify their values. Mutators should protect them by filtering bad parameter values before assigning those values to them. Loop counters and other helper variables should be declared as instance variables so that such counters and helpers don't have to be re-declared local to every member method, individually.