Mercury is a very hot planet—much closer to the sun than Earth. Despite this, many astronomers believed that Mercury had ice on its surface. The way that Mercury orbits the sun leaves the poles of the planet untouched by the sun. In fact, craters at the northern and southern poles are always in the shade and very cold. They could be as cold as -300 degrees Fahrenheit (-185 degrees Celsius)! A probe named MESSENGER visited Mercury in 2012. Sure enough, the spacecraft observed patches of ice in the depths of craters.

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The _________ was correct.

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A memory
B theory
C overseer
D strategy