Read the passage below. 'Mammoth Cave is formed in limestone. Rainwater absorbed carbon dioxide from decaying plants, creating a weak acid. Over a very long time, that water seeped underground and dissolved limestone, opening passages and chambers.' What is the main idea of the explanation?

Read the passage below before answering the question. 'Cumberland Falls, located near Corbin, Kentucky, is often called the Little Niagara of the South. Standing 68 feet tall and 125 feet wide, the waterfall plunges into the Cumberland River with a thunderous roar. On nights with a clear sky and a full moon, a rare natural phenomenon occurs: a brilliant lunar rainbow, or moonbow. Mist rising from the roaring falls refracts the moonlight, producing a delicate arc of shimmering color across the night sky. Cumberland Falls is one of the only places in the Western Hemisphere where moonbows appear predictably on a regular basis.' According to the passage, what environmental conditions are needed for a moonbow to appear at Cumberland Falls?

Read the passage. 'Cumberland Falls is a powerful Kentucky waterfall. On clear nights near a full moon, mist from the falls can refract moonlight and form a rare moonbow. The phenomenon can be seen there on a predictable schedule when conditions cooperate.' Which summary best captures the key information?

Read the passage below before answering the question. 'In the early 1800s, before steamboats dominated the rivers, Kentucky farmers relied on flatboats to transport goods to market. These sturdy, wooden, flat-bottomed craft floated down the Ohio and Mississippi Rivers toward New Orleans. Crew members guided the heavy boats using long oars called steering sweeps. The journey took over a month and was filled with hazards like hidden sandbars, swift currents, and unpredictable weather. Upon reaching New Orleans, farmers sold their corn, tobacco, and cured meats. Because rowing a heavy flatboat upstream against the current was impossible, farmers dismantled the wooden boats and sold the lumber before walking or riding horses back home along the Natchez Trace.' What type of boat did Kentucky farmers use in the early 1800s to carry goods downstream?