If You Measure the Magnetization of an Area of Igneous

If you measure the magnetization of an area of igneous rocks and find a large negative anomaly,what does that imply about the rocks?

A) They were formed during a time of normal polarity of the magnetic field.
B) They were formed during a time of reversed polarity of the magnetic field.
C) They were formed on the ocean floor where the rocks are closer to the core.
D) They were formed on the continental crust in a complex pattern of magnetization.