The question isn't asking which references are equal. The question would use == (double equals) if it were asking about equality. In any case, none of those would be true because they all refer to different object instances.
What the question
is testing is if you understand a legal assignment. If you have a Cat variable, you can't assign a Dog object to it. If you had an Animal reference, you could assign either a Cat or a Dog to it, assuming Cat and Dog both extend Animal (or implement Animal if Animal is an interface). In some cases, you know the type of object is a Cat even though you're currently using an Animal reference to point to it - so you could legally cast the variable to a Cat and then point to it using an actual Cat variable. I'm sure your book explains how all this works in more detail.