题目

质量为m的物块始终固定在倾角为θ的斜面上，如图所示，下列说法中正确的是     A．若斜面向右匀速移动距离s，斜面对物块没有做功     B．若斜面竖直向上匀速移动距离s，斜面对物块做功mgs     C．若斜面向左以加速度a移动距离s，斜面对物块做功mas     D．若斜面竖直向下以加速度a移动距离s，斜面对物块做功m（g +a）s Mr Brown was going away for a week.Before he left,he said to his son,“If anyone asks for me,you can tell him that your father has been out for doing something,and will be back in a week,then be sure to ask him to sit down for a cup of tea.”“OK,Dad,” said his son.But he was afraid his son couldn’t remember this,he wrote these words down on a piece of paper and gave it to him.His son put it into his small pocket,took it out and looked at it every now and then. Four days passed,but no one came to see his father.The boy thought that there was no man to come and that the piece of paper was of no more use for him,so he burnt it that evening. The next afternoon,someone knocked at the door.The boy opened it.A man was standing at the door and said,“Where is your father?” The boy put his hand into his pocket at once and looked for the piece of paper.He could not find it.He suddenly remembered he had burnt it,so he shouted,“No more.” The man was very surprised.He asked,“No more? I met your father last week.When did it happen?”“Burnt yesterday evening.” (    )1.Mr Brown told his son that________. A.he would be away from home for four days B.he would be back in seven days C.he would be back in a month D.he liked a cup of tea (    )2.Mr Brown wrote the words down on________. A.the wall                                                       B.the door C.a piece of paper                                           D.his son’s pocket (    )3.A man came to visit the boy’s father on________. A.the second day                                             B.the third day C.the fourth day                                              D.the fifth day (    )4.The man was very surprised because________. A.he thought the child’s father was dead B.the child didn’t ask him to sit down C.the child gave him a cup of tea D.he couldn’t find that piece of paper (    )5.What was burnt? A.The piece of paper.                                      B.Mr.Smith. C.The visitor.                                                  D.The boy.