which one of the following choices is the correct way to declare a class"Bird" which specifies an abstract "flies" method that returns a boolean?

1. public abstract class Bird {

public abstract flies() { return true;}

}

2. public abstract class Bird {

public abstract boolean flies() { return true;}

}

3. public abstract class Bird {

public abstract boolean flies();

}

4. public abstract class Bird {

public abstract flies();

}

5. public class Bird {

public abstract boolean flies();

}