Which pieces of code inserted independently into places marked 1 and 2 will cause the program to compile and display: 0

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Which pieces of code inserted independently into places marked 1 and 2 will cause the program to compile and display: 0 1 2 3 4 5 6 7 8 9? Choose all that apply.#include <list>#include <iostream>using namespace std;class A { int a; public:A(int a){ this?>a=a;}//insert code here 1};//insert code here 2template<class T> void print(T start, T end) {while (start != end) {std::cout << *start << " "; start++;}}int main() {A t1[] ={ 1, 7, 8, 4, 5 };list<A> l1(t1, t1 + 5);A t2[] ={ 3, 2, 6, 9, 0 };list<A> l2(t2, t2 + 5);l1.sort();l2.sort();l1.merge(l2);print(l1.begin(), l1.end());print(l2.begin(), l2.end()); cout<<endl;return 0;}

A. place 1: operator int() { return a; }
B. place 1: operator int() { return a; } bool operator < (const A & b) { return this?>a< b.a;}
C. place 1: bool operator < (const A & b) { return this?>a< b.a;}
D. place 1: bool operator < (const A & b) { return this?>a< b.a;} friend ostream & operator <<(ostream & c, const A & a); place 2: ostream & operator <<(ostream & c, const A & a) { c<<a.a; return c;} E. place 1: bool operator < (const A & b) { return this?>a< b.a;} place 2: ostream & operator <<(ostream & c, const A & a) { c<<a.a; return c;}