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Generics

 
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Anyone expalin this code . This is from generics from K & B book
public static <T> void addandDisp(Collection<T> cs, T t)
{
for (T o : cs)
{
s.add(o);
}
for (T o : cs)
{
System.out.println(o);
}
}

//call 1
List<? super Object> ls1 = new LinkedList<Object>();
addandDisp(ls1,new String());

//call 2
List<? extends Object> ls2 = new LinkedList<Object>();
addandDisp(ls2,new Object());

//call 3
List<Object> ls3 = new LinkedList<Object>();
addandDisp(ls3,new String());

//call 4
List<? super Object> ls4 = new LinkedList<Object>();
addandDisp(ls4,new Object());

Which call(s) to above method(addandDisp) are error free?

a)only 3

b)only 1 and 3

c)only 1 and 4

d)only 1,2 and 3

e)only 1,3 and 4

Thanks in advance
 
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