关于水平气压梯度力的说法不正确的是（　　）

 如图所示，用手沿竖直方向匀速拉一个动滑轮，使挂在下面重为G的物体缓慢上升，动滑轮的重力不可忽略，现改变物体的重力G，则动滑轮的机械效率η与物体重力G的关系可能符合下列图中的（　　）

   In many high schools，there are strict rules about using mobile phones. If your phone rings in class，for example，the teacher will be very angry.
   Every mobile phone has a ringtone (铃声). It tells you that someone is calling you. Now，there is a ringtone called “mosquitotone (蚊子铃声)”. Using it，students can receive calls and text messages (短信) in class but the teacher will not realize what is happening. How?
   Mosquitotone has a special sound. Only children and teenagers can hear it. As we get older，we are unable to hear some sounds with high frequencies (频率). As a result，a child or teenager can hear the mosquitotone ringtone, but it's_inaudible_to someone 20 or older.
   But sometimes，people over 20 can hear the ringtone. One British student's phone uses mosquitotone. In class，the student's phone rang. The 32­year­old teacher looked at the student and became unhappy. “I heard that. You know the rule：no mobile phone in class.”
   Not all the students are interested in mosquitotone. Jerry Jones，a high school student of 17，says，“Using mosquitotone too often is bad for our hearing. I may use it for pleasure，but not in class. It's unfair to the teachers！”
   What do parents think of mosquitotone？“I think it is perfect for places like movie theaters，” says Connie Neeson,44.“Think about it. Yon're watching a film and someone's mobile phone rings. Mosquitotone is good because many people don't hear it. However，it also has a bad influence on their study if students use it in class.”

    City College Union Inc

    Secretary/Typist

The Union is a student-run organization with a permanent staff of 20. Typing speed: at least 60 wpm.

    The ability to take shorthand dictation and a working knowledge of filling procedures are essential requirements.

    The basic salary for the position is $ 18,500 per year.

    Enquires to R. Barbar 387-5075.

    Emu Airline

    Secretary

    Emu Airline is now offering a part-time position for a secretary.

    The position offers at least 20 hours' work a week, with a view to full-time work in the future.

    Monthly salary is about $ 1,400.

    Phone 899-3264 for an appointment.

    Word Processor

    Operator (full-time)

    We need an operator to work in an office associated with the building industry. Only experiencedoperators are expected to apply.

Starting salary: $ 17,950 yearly.

    Apply in writing to:

    The Personnel Officer Hill Morgan Pty Ltd 38 Green Hill Rd. Kensington 2033.

    Sewing Machinist Wanted

    Jeans Industry

    We are an expanding clothing company located south of the city. Our products include jeans, skirts, shorts and so on. We are looking for sewing machine operators

    The factory works a 38-hour week over 4-5 days. Wages for this are $ 18,050 per year. Wages and conditions are in line with the current industrial award.

    If you are interested, come over and pick up an application form from Ripper Jeans, 23 North Ave, Beaudesert.