A. Often written anonymously - If it is anonymous we don't know who the author is and therefore don't know if they have good knowledge on the subject they are writing about. This isn't a credible source.
B. Published in books - If information is published in books that means that the information is verified. This is because people who have written books a most likely experts. In order for books to be published publishers/editors have to fact check it before it can be given to the public. With so many people reviewing the information there is a lower chance of having inaccurate information.
C. Contains up-to-date information - This was a close second to B, but since up-to-date information is likely just discovered, it may be wrong. There might not have been enough time to properly verify the information before releasing to the public. This isn't a credible source
D. Full of easily identifiable claims - This means that it is full of common sense knowledge. Anyone, even people with limited knowledge of the field, can write about it, if it is that "easy." This isn't a credible source.
Hope this helped!