单选题 有如下类声明：
class Base {
protected:
int amount;
public:
Base(int n=0): amount(n) {}
int getAmount()const {return amount;}
};
class Derived: public Base {
protected:
int value;
public:
Derived(int m, int n): vahle(m), Base(f1) {}
int getData()const {return value+amount;}
};
已知x是一个Derived对象，则下列表达式中正确的是______。