Final answer:
The correct approach to adjusting for magnetic variation is to subtract the variation for an eastern magnetic variation and add for a western magnetic variation when determining magnetic course from true course.
Step-by-step explanation:
The question asked pertains to magnetic variation, which is the difference between magnetic north and true north. When navigating, it is necessary to correct the course for this variation to ensure accurate travel along a desired path. The correct answers for the question 'Eastern magnetic variation is ______ and Western magnetic variation is ______ to/from true course to get magnetic course' are C) subtracted, added.
For an eastern magnetic variation, you subtract the variation from the true course to get the magnetic course, whereas for a western magnetic variation, you add the variation to the true course.