Given the following two classes:

How should you write methods in the ElectricAccount class at line n1 so that the member variable bill is always equal to the value of the member variable kwh multiplied by the member variable rate?
Any amount of electricity used by a customer (represented by an instance of the customer class) must contribute to the customer's bill (represented by the member variable bill) through the method useElectricity method. An instance of the customer class should never be able to tamper with or decrease the value of the member variable bill.

Given the code fragments:

Which modification enables the code to compile?
A:

B:

C:

D:

Given:

What is the result?

Given the definitions of the Bird class and the Peacock class:

and the code fragment:

Which code snippet can be inserted to print Fly.Dance. ?

Given the code fragment:

What is the result?