In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

This river falls 72 feet at the rapids of the Khone Falls, and its floodwaters often reverse the flow of the Tonle Sap River, which flows into it during the dry season. From its marshy source in the Rup-sa Pass of Tibet it rises as the Za Qu River, flowing generally south through Yunnan Province before reaching the major port Phnom Penh and forming much of Laos' border with Myanmar and Thailand. Known for its great delta, FTP, what is this major river of southeast Asia
Social Science