Uranium-235 is the answer
Organisms used to be classified in the earliest times according to their size. As science progressed, they started getting organized by their physical traits and now they're organized by traits found in their species that are not found in others based on the theory of evolution. They are classified according to how they developed from a starting organism.
Generally, the sun observes a solar cycle of eleven years. In this cycle, there are fluctuations in the activity, such as the ejected levels of solar radiation, and in the appearance of the sun, such as changes in the amount and size of sun spots, solar flares and other phenomena that occur on the sun's surface.
These changes also affect phenomena on earth, especially the auroras.
The correct answer would be D), over millions of years, Pangaea broke apart and drifted to form the seven continents.
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I hope this helps :3