Given the below class, what is the correct syntax of declaring a functor that adds 10 to each of the passed argument?

[answerhappygod]

class Add
{
int x;
public:
Add(int x){
this->x = x;
}
int operator()(int a){
return x+a;
}
};
a) Add add_10(10);
b) Add add_10(10);
c) Add add_10(10);
d) Add add_10(5);