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.
