A robot rolls through an underground mine at the Edgar Mine set of Denver, Colo., Dec. 13, 2017. The U.S. Environmental Protection Agency is considering robots and other technologies to investigate abandoned or inactive mines to learn what needs to be done with contaminated water spilling out of the mines and into rivers. Many of the mines are poorly understood and dangerous because of bad air and cave-ins. (AP Photo/Tatiana Flowers)
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