Consider the following code snippet: const int x = 5; const int * ptr = & x; which of the following are true about this code snippet? check all that apply. a. the value of x cannot be changed by the ensuing code. b. the value of *ptr cannot be changed by the ensuing code. c. the value of ptr cannot be changed by the ensuing code. d. the second line must initialize ptr; i. e., "const int * ptr" would be invalid.