第3题: [单项选择]______ in progress, conference participants must turn off their cell phones and digital cameras. A. While B. Although C. Ever D. During 参考答案:A 答案解析:逗号前面的部分是“连词+介词短语”做状语的用法,这里空格后是“介词+名词”,如果出现形容词或者分词也是一样的用法。空格内应填入连词,在分词做状语的情况下,有时也可以不出现连词。在“连词+-ing/p.