In the past,people________the air.A.was used to use ice to coolB.used to using ice to coolC.used to use ice to coolD.was used to using ice to cool
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C解析sb. used to do sth. 某人过去常常做某事(但现在不再如此)；sb. be used to doing sth. 某人习惯做某事；sth. be used to do某物被用来干……。故选C。