To find a magnetic compass course from a true course you must apply __________.

Correct Answer: Option A — deviation and variation

To convert a True course to a Magnetic Compass course, one must account for both Variation (the difference between True and Magnetic North) and Deviation (the magnetic influence of the vessel itself). The mnemonic 'Can Dead Men Vote Twice' (Compass, Deviation, Magnetic, Variation, True) guides this conversion process.