Hi, just a tip for future: you are likely to get far better answers on topics and are likely to get the help you need if you provide as many details as you possibly can, for example key quotations, pictures of questions, and, most importantly, from which book you are referring to. If you still require help with this question, feel free to respond to me and provide me with full details and I will gladly support you with this question.
Hope this is helpful in future.