Why does the author include the information that "the magnetic north and south poles of the Earth switch on the average twice every million years"? A. To provide evidence showing that Earth's protective barrier is difficult to get through B. To show that it is reasonable to think that particles from a supernova explosion could have reached Earth C. To explain why some scientists believe a supernova explosion may have occurred near our solar system D. To help explain why some scientists have rejected the theory presented in paragraph 2