What technology can make coal a cleaner fuel? fluidized-bed combustion building smoke stacks taller implementing a prewash of coal prior to combustion using lower quality, high sulfur coal mixing coal with natural gas to create a hybrid fuel?

Two metal blocks that have slightly different temperatures are placed next to one another. after five minutes, they both have lower but equal temperatures. according to the law of conservation of energy, what  most likelyhappened? energy was created inside the blocks.energy was destroyed inside the blocks.energy was absorbed into the blocks from outside the system.energy was transferred from the warmer block to the cooler block.