Constructed in sections over several centuries beginning in the third century BCE, the Great Wall is the most famous monument in China. The oldest sections of the wall are believed to have crumbled away completely. Modern mapping technologies have revealed parts of the wall that had been absorbed by the landscape. Hills and rivers had hidden sections of the wall over the years. Today, many other elements also threaten the structure. Sandstorms nibble away at some portions of the Great Wall. Tourists also do damage, as some sections draw hundreds of thousands of visitors annually. People's shoes wear down the stone, and many bricks have been carved with people's names. Do It! Human activity is _________ the Great Wall. Press enter to interact with the item, and press tab button or down arrow until reaching the Submit button once the item is selected A infecting B promoting C sustaining D eroding
