题干

A person who has slept well will have a clear mind and work efficiently in the daytime
______ people with sleep disorders find it difficult to concentrate during the day.
A.unlessB.while
C.ifD.until
上一题 下一题 0.85难度 单项选择 更新时间:2015-07-03 05:21:48

答案(点此获取答案解析)