Answer:
Option D
Explanation:
(D) The second part of the sentence says that anyone who reads the ambassador's papers slowly and attentively will be richly repaid. The fact that one should read the papers slowly and attentively for getting the full benefit from them implies that what is contained in them is difficult material.
Among the choices, 'The ambassador's papers are not easy reading' is what brings out this meaning clearly and is the answer.
If his papers are not valuable or insightful reading, then no one can be richly repaid by reading them. So, (B) and (C) are wrong. The phrase 'petty reading' is not appropriate for an ambassador's papers.
