Lord's would provide the serf with housing, farmland, protection, and the serf would care for lords land animals or anything else
The Inca developed important medical practices, including surgery on the human skull. In such operations, they cleaned the area to be operated on and then gave the patient a drug to make him or her unconscious—procedures similar to the modern use of antiseptics and anesthesia.
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The correct answer is B.
The development of cheap iron in the US was the major factor that lead to the building of skyscrapers. Being able to produce iron cheaply can be contributed to Andrew Carnegie. This American business mogul perfected the Bessemer process in several factories across the eastern part of the US. From there, he was able to sell cheap iron to American businesses for the purpose of growing their empire.