有如下程序：
#include ＜iostream＞
using namespace std;
class Base

private:
char c;
public:
Base(char n):c(n)
～Base()

cout＜＜c;

；
class Derived: public Base

private:
char c;
public:
Derived(char n):Base(n+1),c(n)
～Derived()

cout＜＜c;

;
int main()

Derived obj('x');
return 0;

执行上面的程序将输出( )。

A．xy
B．yx
C．x
D．y