C++ quiz. What will be printed as the result of the program?

What will be printed as the result of the program?

#include <iostream>
#include <string>

struct A {
  const std::string &a;
  A(const std::string &b) : a(b) {}
};

int main() {
  A a("test");
  std::cout << a.a;
}

test
Nothing
Undefined behaviour
Code will not compile

Explanation

The result is undefined because the A::a reference will point to a temporary variable created in line 2 and deleted there. Therefore, the result of the program is not defined after this line. An execution error may or may not occur in line 3, since undefined behaviour