学习了奥斯特实验后，小军和小民认为：通电的螺线管周围也存在磁场．可是，通电螺线管周围的磁场是什么样的呢？

为此，他们找来器材并连成了图甲所示的实验电路，运用研究磁场的方法来探究通电螺线管外部的磁场．

I like to eat       ．

B

    It's 14:00. The house is quiet(安静的). "Tom?" Mom says. No one answers.

    Mom comes to Tom's house. He is not in the bed. But his model plane is on the desk. "He is not in his room, and he is not in the yard(院子)," Mom thinks. Then Mom comes to his grandparents' room. Tom likes to play with Grandpa's tape player. But he is not there.

    Mom looks for(寻找) him everywhere. But where is Tom? Mom is worried. She wants to call Dad. She comes to the living room to get the phone.

    "What's that?" Mom sees something(某物) black under the sofa. Oh, it's Paul, Tom's dog. It loves sleeping(睡觉) there. But what is next to Paul? It's Tom!