What Are the Van Allen Belts

What are the Van Allen belts?

A) two doughnut-shaped regions of high-energy charged particles in Earth's magnetosphere
B) oval-shaped region around each of Earth's magnetic poles where charged particles collide with ions in Earth's atmosphere
C) inner and outer parts of the asteroid belt
D) regions of high concentration of electrons and ionized atoms in Earth's upper atmosphere where radio waves are reflected toward the surface of Earth