Consider the following code snippet: public abstract class Machine { public abstract void setRPMs(); . . . } You wish to create a concrete subclass named PolisherMachine. Which of the following is the correct way to declare this subclass?a. public class PolisherMachine implements Machine { public void setRPMs() { . . . } } b. public class PolisherMachine extends Machine { void setRPMs() { . . .} } c. public class PolisherMachine implements Machine { void setRPMs() { . . .} } d. public class PolisherMachine extends Machine { public void setRPMs() { . . . } }