While preparing for the SCJP-6 exam I faced with a difficult issue. I can’t find answer by myself. Please, answer for the question and give short comments:

abstract class A<K> extends Number> {
   // insert code here
}    

1. public abstract <K> A<? extends Number> useMe(A<? super K> k);

2. public abstract <K> A<? super Number> useMe(A<? extends K> k);

3. public abstract <K> A<K> useMe(A<K> k);

4. public abstract <V extends K> A<V> useMe(A<V> k);

5. public abstract <V super K> A<V> useMe(A<V> k);

6. public abstract <V extends Character> A<? super V> useMe(A<K> k);

7. public abstract <V super Character> A<? super V> useMe(A<K> k);

Which method can be inserted in a placeholder above?

P.S. I tried to look on the specification. Those one was not helpful for me.