given classes MyBase and MySub such that MySub is a subclass of MyBase, which line(s) if any cause a compiler error? Which line(s) if any cause a ClassCastException... 1. MyBase objBase = new MyBase(); ok 2. MySub objSub = new MySub(); ok 3. objBase = objSub; ok 4. objSub = obj ??? consider obj is a object of class Object 5. objBase = (MyBase)objSub;?? 6. objSub = (MySub)objBase;???