The correct answer is A. The address of a variable.
A pointer is a variable that stores the address of another variable. It is used to access the value of the variable that it points to. For example, if x is a variable, then &x is a pointer to x. The value of &x is the address of x.
B is incorrect because a pointer is not an indication of the variable to be accessed next. A pointer is simply a variable that stores the address of another variable. It is up to the programmer to decide how to use the pointer.
C is incorrect because a pointer is not a variable for storing addresses. A pointer is a variable that stores the address of another variable. It is not a variable for storing addresses in general.
D is incorrect because a pointer is not the data type of an address variable. The data type of an address variable is pointer.