多选题 Given:
5. abstract class Thing {static String s = ""; Thing() {s += "t "; } }
6. class Steel extends Thing {
7. Steel() {s += "s "; }
8. Steel (String s1) {
9. s += s1;
10. new Steel();
11. }
12. }
13. public class Tungsten extends Steel
14. Tungsten(String s1) {
15. s += s1;
16. new Steel(s);
17. }
18. public static void main(String[] args) {
19. new Tungsten("tu ");
20. System.out.println(s);
21. } }
What is the result?