【题目】It is so cold that you can't go outside _____ fully covered in thick clothes.
A.if
B.unless
C.once
D.when

【答案】B
【解析】句意：外面太冷了，你不要出去，除非用厚衣服完全裹起来。A项”如果“；B项”除非“;C项”一旦“；D项”当....时“。”unless fully covered“为”连词+省略结构“补充完事为”unless you are“。故选B项。