Identify the true statement. a. All polarity chrons are the same length of time; they differ only in the magnetic strengths they represent. b. The series of rock stripes perpendicular to and bilaterally symmetric across the mid-ocean ridge records the sequence of the Earth's magnetic reversals over time. c. The width of each rock stripe is a measure of how long the polar direction took to change. d. Positive magnetic anomalies occur over areas of seafloor when the poles of the Earth's magnetic field and the paleopoles preserved in the seafloor basalt agree.