Select all options that declare a constant pointer

Select all options that declare a constant pointer (i.e. a pointer which value cannot be changed)

const int * a;
int const * a;
int * const a;
const int * const a;
None of the above

Mnemonic rule: read the pointer declaration from right to left.
For example:
int * i; // pointer to int
int * const i; // constant pointer to int
int const * i; // pointer to a constant of type int
int const * const i; // constant pointer to a constant of type int