OIC NAVIGATIONAL WATCH: Index error of a sextant is primarily caused by ___________.

Index error of a sextant is primarily caused by ___________.

A.improperly correcting the errors in the sextant
B.the horizon glass not being parallel to the horizon mirror
C.human error in taking the celestial observation
D.the horizon glass not being parallel to the index mirror

Answer: 


D.the horizon glass not being parallel to the index mirror