What have observed more than 50,000 asteroids

Explanation:

More than 50,000 meteorites have been found on Earth. Of these, 99.8 percent come from asteroids. The remaining small fraction (0.2 percent) of meteorites is split roughly equally between meteorites from Mars and the Moon. The over 60 known Martian meteorites were blasted off Mars by meteoroid impacts.

More than 50,000 meteorites have been found on Earth. Of these, 99.8 percent come from asteroids. The remaining small fraction (0.2 percent) of meteorites is split roughly equally between meteorites from Mars and the Moon. The over 60 known Martian meteorites were blasted off Mars by meteoroid impacts.    

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i believe the answer is a or 1