Output of following C++ program?#includeusing namespace std;int main(){ int x = 10; int& ref = x; ref = 20; cout << "x = " << x << endl ; x = 30; cout << "ref = " << ref << endl; return 0;}

• A. x = 20; ref = 30
• B. x = 20; ref = 20
• C. x = 10; ref = 30
• D. x = 30; ref = 30