单项选择题
有下列程序： #include＜iostream＞
Using namespace std; Class Amount{
int amount;
public; Amount(int
n=O):amount(n){} Int
getAmount()const{return amount;}
Amount &operator+=(AmountA) {
amount+=a.amount;
return }
}; int main(){
Amount x(3),y(7);
x+=y;
cout＜＜x.getAmount()＜＜endl;
return 0; }
己知程序的运行结果是10，则横线处缺失的表达式是 。
A. *this
B. this
C. &amount
D. amount