다음 C++ 프로그램의 실행 결과로 옳은 것은?

#include <iostream>
using namespace std;

class Student {
public:
 Student() : Student(0) {};
 Student(int id) : _id(id) {
 if (_id > 0) _cnt++;
 };
 static void print() { cout << _cnt; };
 void printID() { cout << ++_id; };
private:
 int _id;
 static int _cnt;
};

int Student::_cnt = 0;

int main() {
 Student A(2);
 Student B;
 Student C(4);
 Student D(-5);
 Student E;
 Student::print();
 E.printID();
 return 0;
}