多选题 Given:
1. import java.util.*;
2. public class Ps {
3. public static void main(String[] args) {
4. PriorityQueue＜String＞ pq = new PriorityQueue＜String＞();
5. pq.add("4");
6. pq.add("7");
7. pq.add("2" );
8. // insert code here
9. } }
Which code fragment(s), inserted independently at line 8, produce the output "2-4-7-"? (Choose all that apply.)

A、 Iterator it2 = pq.iterator();while(it2.hasNext()) System.out.print(it2.next() + "-");System.out.println();
B、 Arrays.sort(pq.toArray());Iterator it3 = pq.iterator();while(it3.hasNext()) System.out.print(it3.next() + "-");System.out.println();
C、 Object[] pqa = pq.toArray();Arrays.sort(pqa);for(Object o: pqa) System.out.print(o + "-");System.out.println();
D、 String s = pq.poll();while (s != null) {System.out.print(s + "-");s = pq.poll();}
E、 String s = pq.peek();while (s != null) {System.out.print(s + "-");s = pq.peek();}

【正确答案】 C、D

【答案解析】