As the sea ice melts sooner each swimmer polar bears are forced to come ashore earlier and

问题补充：

As the sea ice melts sooner each swimmer,polar bears are forced to come 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

答案：

(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。