Which of the listed code fragments contain errors:

struct A {
    operator int() { return 0; }
};

struct B { 
    operator int&() { return 0; } 
};

struct C { 
    static int i; 
    operator int&() { return i; } 
};

Explanation

A - it's okay, there's a type conversion operator declared here.
B - it is impossible to return the reference to a temporary constant variable.
C - everything is fine, here the operator of transformation of type which returns the reference to a static variable is declared