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. before
B. unless
C. since
D. until
网友回答
(答案→)A. before
B. unless
C. since
D. until
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。