Question: Generics

Given:

// insert code here
private N min, max;
public N getMin() { return min; } 
public N getMax() { return max; }
public void add(N added) {
 if (min == null || added.doubleValue() < min.doubleValue())
 min = added;
 if (max == null || added.doubleValue() > max.doubleValue())
 max = added;
 }
}

Which two, inserted at line 11, will allow the code to compile? (Choose two.)
A. public class MinMax<?> {
B. public class MinMax<? extends Number> {
C. public class MinMax<N extends Object> {
D. public class MinMax<N extends Number> {
E. public class MinMax<? extends Object> {
F. public class MinMax<N extends Integer> {

Execution:
 Yet to study...

Answer:
D. public class MinMax<N extends Number> {
F. public class MinMax<N extends Integer> {