article: This is a letter from a pet dog to his master .
  "Dear master, when you took me away from my mum, it was snowing heavily. You kept me in your arms, and that made me feel very warm and comfortable. I've been with you for about a year so far, but I'm afraid you don't know me quite well, so I decide to write this letter to you.
  I'll live for ten to fifteen years before leaving this world. I enjoy every moment being with you. So I'm always sad when I stay away from you.
  Please give me time to understand what you want me to do. Don't lock me up if you are angry with me. Don't leave me alone all the time. You have your work and your friends. But I only have you.
  Talk to me sometimes. Although I don't understand your words, I can tell from your voice whether you are happy or sad. Please don't treat me badly when you are unhappy. Remember that: however you treat me, I will never forget it. And if you treat me terribly, it will have a bad influence on me for a long time.
  Before you hit me, remember that I have _ teeth that could easily hurt you, but that I choose not to. You are my master, I can never hurt you.
  Take care of me when I get old. You will grow old, too.
  One day I might leave you forever. However, everything will be easy for me if you are there. Please keep in mind: I love you, always."
question: The pet dog will never forget  _  .
options: its master's voice its master's words how its master treats it its master's name