单项选择题
（）so many people in the United States been out of work as today.
A.More than ever before B.In the past, there have never C.Never before have D.Formerly, there never were
单项选择题 When he suddenly（） up the subject of genetic engineering, there was an embarrassed silence.
单项选择题 The problem（）when the students refused to do their homework.
单项选择题 Speaker A: Want to come over Thursday for supper? Speaker B:（）
