【题目】_______relevant departments stressed no plastic covers were used for books, I didn't realize these covers contained harmful chemicals.
A.UntilB.UnlessC.WhileD.Since
在线课程【答案】A
【解析】
考查连词。句意：直到相关部门强调书不能使用塑料封面，我才意识到这些塑料封面含有有害的化学物质。A. Until直到；B. Unless 除非；C. While尽管；D. Since自从。分析句子可知，此处考查固定句型not…until…“直到……才……”，故选A项。