The one answer that I am missing among the options, but which is the correct one is: the geography of the region ( I assume that that's what was instead of the "7" in the first option).
It was very mountainous, with valleys and islands on which people lived -meaning there was a natural separation between the different settlements.
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Answer and Explanation:
Student B is correct, because Mercury is, in fact, possible to be visualized during the morning or evening twilight, that is, just after sunset, or just after sunrise, as times are necessary for the planet earth it has the right lighting to visualize it.
Student C is the one that is most incorrect, because at midnight the planet earth has very low luminosity so that Mercury can be visualized. Since it needs a low illumination, however existent for the planet Mercury to be seen.
Out of the choices given, the boundary of eras marked by a great worldwide changes in life forms. The correct answer is B.