Which of the following is true of a rock that has the property of paleomagnetism?
a. rocks formed millions of years ago show the location of the magnetic poles at the time of their formation.
b. all rocks, regardless of when they are formed, will eventually possess the same polarity.
c. a major shift in polarity occurred in all rocks that were formed one million years ago.
d. a rock possesses a specific polarity depending on where it is formed.