The correct answer is C. constant.
A constant is a variable whose value cannot be changed during the execution of a program. It is declared using the keyword const. For example,
const int x = 10;
The value of x cannot be changed after it is declared.
A numeric variable is a variable that can store a number. It is declared using the keyword int, float, or double. For example,
int x = 10;
float y = 3.14;
double z = 6.02214179e23;
A string variable is a variable that can store a sequence of characters. It is declared using the keyword string. For example,
string s = "Hello, world!";
None of the options A, B, and D are correct.
