Could you help me with this:

Question A.1 Justify All Answers (3 Points Each Part) (a) Why are static methods are not allowed to use the Java keyword this. (b) Give an example of a mutable object, and an example of a non-mutable object. (c) How can you create a class whose instances are non-mutable? (d) What is the signature of a method? (Ilustrate) e) How is the concept of a signature used? (f) Suppose BB is a subclass of AA. If aa and bb (respectively) are instances of AA and BB, which of these assignments are valid: aa-bb or bb-aa. Explain why this makes sense