【题目】The researchers ______ till midnight every day since the outbreak of the disease to find an effective cure.
A.workB.will work
C.are workingD.have been working
在线课程【答案】D
【解析】
考查时态语态。句意：自从疫情爆发以来,研究者毎天都忙到深夜以找到有效的治愈方法。 时间状语since the outbreak of the disease提示用完成时态, till midnight表示动作的持续性,故用现在完成进行时,故选D。