4. [2 points] The following problems all involve three distinct classes, A, B, and C. a. Suppose that the following code compiles and runs without any exceptions. What can you say about the relationship between the classes A, B, and C? A x1 = new C(); B x2 = x1; B x3 = (B) x1; B x4 = (C) x1; b. Now suppose the code in part (a) fails to compile, but if we remove the second line it compiles and runs without any exceptions. What can you say about the relationship between the classes A, B, and C? c. Now suppose that the code in (a) fails to compile, and when we remove the second and fourth lines it compiles, but causes a ClassCastException at runtime. What can you say about the relationship between the classes A, B, and C?