Statement: Whenever you have any doubt on this subject, you may refer to the book by Enn and Enn.
Assumptions:
1. The book by Enn and Enn is available.
2. There is no other book on this subject.
Answer: A
The recommendation of the book by Enn and Enn implies that it is available. So, I is implicit. Also, the book has been referred to as a good one, but this does not mean that no other books are available on the subject. So, II is not implicit.