23. Using call-by-value for the copy constructor's parameter a. is necessary to prevent it being modified b. causes a recursive runaway when the copy constructor is called c. has no harmful effects other than the copy overhead d. makes sense if the parameter is a scalar (primitive) 12. To maintain semantic consistency, one might a. define + in terms of += b. define in terms of an int-valued compare function c. define is Empty in terms of a s ize function d. all of the above 13. Having the () (subscript) operator return a reference (e.g. Int s) a. is a bad idea b. is illegal in CH+ c. allows the [] to appear as the left operand of an assignment operator d. only makes sense if the subscript index is an integer e. can only be done if the index was passed as by-reference as well 14. Given that + has been overloaded as a member function (with an int parameter) of a class c, which of the following is a legal call, given a variable el of class c a. operator +(c1,12) b. +(cl,12) c. c1.+(12) d. c1. operator +(12)