Certain Metallic Crystals Leave a Record of the Polarity of the Earth

Multiple Choice

Certain metallic crystals leave a record of the polarity of the earth at the point in time when they were formed in molten rock because they:

A) leave radioactive "signatures" that scientists can read
B) act as small magnets that orient themselves to the poles before the rock solidifies
C) form ring-type patterns like tree rings that can be counted
D) contain amino acids which form as crystals,and this change in the amino acids can be used to determine the passage of time