有以下程序：#include ＜iostream＞using namespace std;class sample{private: int x; static int y;public: sample(int a); static void print(sample s);};sample:: sample(int a){ x=a; y+=x;}void sample:: print(sample s){ cout＜＜"x="＜＜s. x＜＜",y="＜＜y＜＜end1;}int sample:: y=0;int main(){ sample s1(10); sample s2(20); sample:: print(s2); return 0;}程序运行后的输出结果是( )。

A．x=10,y=20

B．x=20,y=30

C．x=30,y=20

D．x=30,y=30