Confused with Actionscript basic concepts

Hi i am new to this forum as well as Actionscript.

I’ve got this book- OReiley Essentials Actionscript 3.0

and extracted from page 40 of the book:

package zoo {
public class VirtualZoo {
private var pet;
public function VirtualZoo ( ) {
this.pet = new VirtualPet(“Stan”);
this.pet.getAge( );
}
}
}

i would like to ask if ‘this’ in this.pet refers to which object VirtualZoo or VirtualPet?

Thanks!