My C++ Quiz

Question #19: Which of the following lines should NOT compile?

1 
2 int main()
3 {
4     int a[54] = {};
5 
6     int b[54] = {};
7 
8     int* x = a;
9 
10    int* const y = a;
11 
12    b = x;
13 
14    b = y;
15 
16    return 0;
17 }