Protected modifier

There are four classes within different packages.

Read the source code and pick the legal method calls.

package birds;

/**
 * Bird class
 */
public class Bird {

    public void fly(){
        System.out.println("Goodbye, I'm flying away");
    }

    protected void sing(){
        System.out.println("I'm singing!");
    }
}

// --------------------

package mammals.felines;

import mammals.Mammal;

/**
 * Cat class
 */
public class Cat extends Mammal { }

// --------------------

package mammals;

/**
 * Mammal class
 */
public class Mammal {

    protected void motherChild(){
        System.out.println("My baby was just born");
    }

    void yell(){
        System.out.println("I am a mammal!");
    }
}

// --------------------

package mammals;

import birds.Bird;
import mammals.Mammal;
import mammals.felines.Cat;

/**
 * The main class
 */
public class Main {

    public static void main(String[] args) {
        Cat cat = new Cat();
        Bird bird = new Bird();
        Mammal mammal = new Mammal();
    }
}