“绿色、环保、低碳”是当今世界的关键词，“低碳”要求我们节约及高效利用能源．关于能源与能量，下列说法正确的是（  ）

根据短文理解, 完成下列各题。

      One day, I was cooking with my friend Sandy in the kitchen. Suddenly, Sandy cut her finger. I went to her quickly. But to my surprise, I saw computer chips in her finger.

   “Now you know my secret, you have to die!” Sandy said and picked up the knife. “No, please, Sandy. Aren't we good friends?” I shouted. But before Sandy could say anything, she fainted.

    “Oh, Sandy!” I took her to hospital in a hurry. After a doctor checked her, he said, “I'm afraid we can't help her. Why don't you take her to a robot centre?”

      I hurried to a robot centre. A few days later, Sandy was well. She asked, ”Mary, why did you save me even after I tried to kill you? ”

“Because I'm sure you are my friend. Can you tell me where you are from?” “I'm from another planet. It's far from here. Thank you, my friend Now I see how friendly people are on the earth.”

      Two days later, a UFO came and picked her up. Since then I've never seen her.

若要研究通过导体的电流与导体两端电压的关系，除了图示器材外还需要：电源(恒压)、开关、导线、____ ，同时应将小灯泡换成定值电阻，理由是____ 。