如下图所示的四种测量器具中，不能直接测量物体质量的器具是（　　）

联通公司手机话费收费有A套餐（月租费15元，通话费每分钟0.1元）和B套餐（月租费0元，通话费每分钟0.15元）两种．设A套餐每月话费为y₁（元），B套餐每月话费为y₂（元），月通话时间为x分钟．

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    Hi, I'm Tom. I'm a student. I'm eleven. My birthday is on 12th July. I go to school by bike. My father is a fireman. He uses water to put out fires. He's brave. He goes to work by bus. My mother is a doctor. She works in a hospital. She helps people. She goes to work by car. I like helping people, too. I want to be a doctor in the future. But my brother wants to fly a plane. He wants to be a pilot in the future.