SAT English Practice Question

The main purpose of the passage is to argue that it’s difficult to know when the Earth’s magnetic field will reverse. The author emphasizes this point by noting that the field has reversed “hundreds of times” in the past but that “no one knows for sure” when the next reversal will occur. The author also acknowledges that the field is changing right now, suggesting that a reversal could be occurring soon. In the following passage, the author’s main purpose is to

1. A.To provide evidence that the Earth’s magnetic field is unpredictable.
2. B.To contrast the Earth’s magnetic field with other natural phenomena.
3. C.To discuss the history of the Earth’s magnetic field.
4. D.To explain how the Earth’s magnetic field is changing.