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

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

   public void method3()
   {  method4(new Test());
   }

   public void method4(Test aTest)
   {  aTest.method1(17);
   }

   private int x = 3;
   private static int y = 10;
}
Some of the methods can, in fact, be class methods (static). Which ones?

(a) method1.
(b) method2.
(c) method3.
(d) method4.

Select all correct answers.