What best describes an agonic line?

• A. A line where magnetic variation is greatest.
• B. A line where geographic poles are opposite magnetic field direction.
• C. An irregular imaginary line where magnetic and geographic poles are aligned and there is no magnetic variation.
• D. A line marking the boundary of magnetic time zones.

Answer: (C)

An agonic line is the imaginary path on the Earth where magnetic variation is zero, so magnetic north and geographic (true) north align. Along this line, a compass points to true north because there is no difference between the two north references. The line is irregular and changes over time as the Earth's magnetic field evolves, not a fixed straight line. That description—an irregular imaginary line where magnetic and geographic poles are aligned and there is no magnetic variation—matches what the agonic line is. The other options describe different, non-existent or unrelated concepts, such as maximum variation or time-zone boundaries, which don’t define agonic lines.