电路如图所示，电流表的量程为0～0.6A，电压表的量程为0～3V，电源电压9V保持不变，滑动变阻器的最大阻值为50Ω，定值电阻R₀为10Ω，S闭合后，在确保电路安全的情况下，正确的说法是 （    ）

What can Tony do?    

    Today is Saturday. In the morning, Xiaoyong is sleeping, but the phone rings. He wakes up from his dream. He gets up and goes to the park near his home. He is doing exercise, but it starts to rain. He has to go home. He is doing his homework at home, but the bell rings.

    In the afternoon, Xiaoyong is riding his bike, but suddenly(突然)a little dog runs to him. He falls off his bike. He is so sad.

 下列叙述中正确的是（　　）

①化学变化不但生成其他物质，而且还伴随着能量的变化

②人类利用的能量都是通过化学反应获得的

③燃料作为重要的能源，对人类社会的发展非常重要

④可燃物在任何条件下燃烧都会发生爆炸

⑤化学反应过程中都会发生放热现象．