Magnetic anomalies are:

A. found only on the seafloor.
B. measured with an instrument called an inclinometer.
C. places where the magnetic field strength is either greater or less than the expected strength.
D. defined as the angle between which a compass needle points and the longitude at that point.

C. places where the magnetic field strength is either greater or less than the expected strength.

Explanation:

Magnetic anomalies are places where the magnetic field strength is either greater or less than the expected strength.

Magnetic anomaly usually occur in rocks that have iron ore mineral or magnetite mineral. It occurs majorly in igneous and metamorphic rocks because of the presence of ferromagnesian minerals in them.

It doesn't usually occur in sedimentary rocks because iron or ferromagnesian minerals have weathered away in them.

Magnetic anomaly also refers to the local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks.The Earth’s magnetic field is composed of varying frequencies of magnetic anomalies.

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