With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Relative to downtown, the city is generally flat with the exception of the area surrounding North street, where a hill of gradually develops approaching from the south and north. The Southtowns include the Boston Hills, while the Appalachian Mountains sit in the Southern Tier below them. To the north and east, the region maintains a flatter profile descending to Lake Ontario. Various types of shale, limestone and lagerstätten are prevalent in the geographic makeup of Buffalo and surrounding areas, which line the waterbeds within and bordering the city. Although there have not been any recent or significant earthquakes, Buffalo sits atop of the Southern Great Lakes Seismic Zone, which is part of the Great Lakes tectonic zone. Buffalo has four channels that flow through its boundaries: the Niagara River, Buffalo River and Creek, Scajaquada Creek, and the Black Rock Canal, which is adjacent to the Niagara River.
text_B: Is the city completely flat?
NO.