What is the tallest skyscraper in the US?

One World Trade Center in NYC

Explanation:

Since its topping out in 2013, One World Trade Center in New York City has been the tallest skyscraper in the United States. Its spire brings the structure to a symbolic architectural height of 1,776 feet (541 m), connoting the year the U.S. Declaration of Independence was signed, though the absolute tip (or pinnacle) of the structure is measured at 1,792 ft (546 m).[3] However, the observation deck elevation and highest occupied floor of One World Trade Center are surpassed by 432 Park Avenue and Chicago's Willis Tower (formerly and still commonly known as the Sears Tower). Steinway Tower, and Central Park Tower will also have higher occupied floors and roofs upon their completion.

C) to abolish the practice of slavery within the United States.