As the sea ice melts sooner each swimmer,polar bears are forced to e ashore earlier and face food shortages _____ they have stored enough fat to last them through the season.A.beforeB.unlessC.sinceD.until
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A解析本题考查连词。句意：因为海冰融化得比游泳者早，北极熊没来得及为整季储存足够的脂肪，就被迫提前上岸，面临食物短缺。before conj.在……之前；比……早些。