继电保护、安全自动装置的工作电源退出，出口连接片断开时的状态是（）
A.投入状态
B.退出状态
C.停用状态
D.断开状态
参考答案：C
阅读理解。
Yesterday Paul had a busy day. In the morning he cooked some noodles for his family. He went to visit
his aunt at 9:30. In the afternoon he played soccer ball with his classmates. After that he cleaned the room
because it was dirty. He was a little tired,but very happy. After dinner he did his homework. Then he watched
TV for about two hours. He went to bed at nine o'clock.
根据短文内容,判断下列句子正(T)误(F).
( )1. Paul had a busy and happy day off.
( )2. In the morning he cooked some hamburgers for his family.
( )3. In the afternoon he played soccer ball with his parents.
( )4. He cleaned his room in the afternoon.
( )5. He watched TV first then he did his homework.
为了研究某种商品年需求量(公斤)和该商品价格(元)之间的关系，以家庭为单位，经随机抽样10个家庭调查获得一组数据，计算得到：
∑X=30，∑Y=20，Lxx=-6，Lxy=8，Lyy=7.5
F1-0.05 (1，8)＝5.32 U0.975=1.96
σ的估计值为（）。
A．3.11
B．0.392
C．0.75
D．1.33
