import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Tester{

	public static void main(String[] args) {

		List<Human> humans = new ArrayList<Human>();
		humans.add(new Human(13));
		humans.add(new Human(33));
		humans.add(new Human(21));
		humans.add(new Human(21)); // line 1
		HumanComparator c = new HumanComparator(); // line 2
		Collections.sort(humans, c); // line 3
		System.out.print(humans.get(0).age);
		Collections.sort(humans); // line 4
		System.out.print(humans.get(0).age);

	}

}

class Human implements Comparable<Human> {
	Integer age;

	public Human(int age) {
		this.age = age;
	}

	public int compareTo(Human h) {
		return h.age.compareTo(this.age);
	}

}

class HumanComparator implements Comparator<Human> {

	public int compare(Human h1, Human h2) {
		return h1.age.compareTo(h2.age);
	}

}
                                

A  line 1 causes a compilation error (no duplicates are allowed)

B  line 2 causes a compilation error, the correct instantiation for HumanComparator is as so :
new HumanComparator<Human>()

C  line 4 causes a compilation error, must supply a Comparator to methos sort.

D  The program compiles and runs fine printing 1333

E  The program compiles and runs fine printing 3313