单项选择题

有以下程序: #include<iostrearn> 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