The following Java class definition compiles, but all its methods are instance methods: 
public class Test
{
   private void method1()
   {  System.out.println(x);
   }

   public void method2(int a)
   {  System.out.println(a);
   }

   public void method3()
   {  method1();
   }

   private void method4()
   {  method2(17);
   }

   private int x;
}
Some of the methods can, in fact, be class methods (static). Which ones?

(a) method1 and method4.
(b) method2 and method3.
(c) method2 and method4.
(d) method1 and method3.
(e) All four methods.

Select the most appropriate answer.