如图所示是小明研究“影响电磁铁磁性强弱因素”的装置图，它是由电源、滑动变阻器、开关、带铁芯的螺线管和自制的针式刻度板组成。通过观察指针B偏转角度的大小来判断电磁铁磁性的强弱。在指针下方固定一物体A，当用导线a与接线柱2相连，闭合开关后，指针B发生偏转。

根据中文、英文解释或句意填空

根据短文内容，判断正确还是错误。

    There is a big fruit shop near Kitty's home. Kitty is at the fruit shop now. There are many kinds of fruits. There are big apples, yellow pears, fresh bananas, juicy oranges, and so on. Kitty wants to buy some apples and bananas. They are expensive. The apples cost ten yuan. The bananas cost twenty yuan.

关于摩擦力，下列说法正确的是（　　）