I don't know how to select a correct answer in this Question

Hi I am not an instructor but I know the answer is found in line 17-22: "The ILC's Draft Articles on the Law of the Non-Navigational Uses of International Watercourses are an attempt to codify the customary principles of international water law as those principles are manifested in past legal decisions and currently accepted international practice. " Since the line reference specifically told us that the principles of ILC draft articles are to codify the customary principles of international water laws, it leads us to the correct answer D which says that treaty structure is a set of general prescriptive principles to be followed in the formulation of the provisions of treaties I hope that I answered it correct. Please feel free to correct me. Thank you

Agreed Jing Jing, I would also note that all of the other answer choices either go way beyond what the treaty does according to the text, or are just not true of the treaty.