The answer is A and b hope it helps
Answer:
Here you go:
Distinct dynasties built different courses of boundary walls. They reach in total from Liaodong in the east to Lop Lake in the west, from the present-day Sino-Russian border in the north to the Tao River in the south, along an arc that roughly delineates the Mongolian steppe's boundary. The Great Wall's protective system is now widely regarded as one of history's most spectacular architectural marvels.
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