关于下列代码说法正确的是：(     )

public interface DoStuff2 {
    float getRange(int low, int high);
}
interface DoMore { 
    float getAvg(int a, int b, int c);
}
abstract class DoAbstract implements DoStuff2, DoMore {}
class DoStuff implements DoStuff2 {
    public float getRange(int x, int y) { 
        return 3.14f; 
    }
}
interface DoAll extends DoMore { 
    float getAvg(int a, int b, int c, int d);
}