$6)$ Which line in the following program will cause a compiler error?

$1$ #include

$2$ using namespace std;

$3$

$4$ int main$()$

$5\{$

$6$ const int MY$\_$VAL $=77$;

$7$ MY$\_$VAL $=99$;

$8$ cout $<<$ MY$\_$VAL $<<$ endl;

$9$ return $0$;

$10\}$

A$)6$

B$)8$

C$)9$

D$)7$