I think the main reason why the Great Wall was rebuilt in the fourteenth century is a will to keep out the Mongolian invaders from the north (answer B). It took place during the Ming dynasty which had quite a big problems with the invasions before.
The Chinese rebuilt the Great Wall in the 1400s primarily to keep out Mongolian invaders from the north, which corresponds to option B. During the Ming Dynasty, fears of Mongolian threats led to significant expansions and fortifications of the wall. The rebuilding efforts were crucial for ensuring the safety and stability of the Chinese territory during this period.
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