多选题 Given:
2. class SuperCool {
3. static String os = "";
4. void doStuff() {os += "super "; }
5. }
6. public class Cool extends SuperCool {
7. public static void main(String[] args) {
8. new Cool() .go();
9. }
10. void go() {
11. SuperCool s = new Cool();
12. Cool c = (Cool)s;
13. // insert code here
14. }
15. void doStuff() { os += "cool "; }
16. }
If the rest of the code compiles, which line(s) of code, inserted independently at line 13, compile? (Choose all that apply.)