The correct answer is D) All of the above. The three sextant errors mentioned - prismatic error, centering error, and graduation error - are all considered nonadjustable errors. These are inherent flaws in the sextant design or manufacturing that cannot be corrected by the user. They are permanent and must be accounted for when taking celestial navigation measurements. In contrast, adjustable errors like index error can be calibrated and mitigated by the user. Therefore, the statement that all three listed errors are nonadjustable is correct.