Seems there is a bug in the registration pages. I own the Cocoa book but for reason it started asking me about the names of the authors of the iOS book. I had to search online for the book and authors to answer the question.
Rob
I will add to this. I do own the iOS book and it asked for the last name of the first author listed. I am using the 4th edition of the book but the question was not updated for that. I happened to also have the 3rd edition and so I tried that one which worked. Perhaps this site should just use Captcha instead of asking these sorts of questions given the variety of books and editions in play. They are obviously not updated.