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。

根据文意及首字母提示补全短文。

      As everyone knows, not o____ fast walk but also slow walk does good to the muscles and lungs of human. So people walk to build up their bodies, or to lose w____. But only some of them know that taking a walk every day is also good for p____ people's hearts. Heart attack has become the first disease in the world b____ more and more people suffer from it.

    Taking a walk can improve the blood supply to our hearts. If you try to walk as o____ as possible, you'll have a healthier heart.