阅读下列短文，从下面每小题的A、B、C、D四个选项中选出最佳选项。

    Ever since I was a child，my mouth has caused me trouble．I'm not a bad person；I have just had a hard time learning when to keep my mouth closed．

My mom has told me again and again，"Robert，your constant bad words are hurting me．If you continue to be this rude，you will get into big trouble．"

    It's been a problem at school several times，too，when teachers have told me something I didn't want to hear．I used to feel it was my duty to stand up for myself and tell them ______ off．

    One day in English class I began working on my homework until I heard a classmate talking behind me．It was Nathaniel，talking to himself as usual．

I said ever so nicely，"Nathaniel，would you be quiet?"

Nathaniel continued talking to himself．I quickly shouted，"Nathaniel，shut up!"

    For the next five minutes，we threw hurtful words back and forth at each other．

"At least I don't have an ugly lazy eye like you!"I shouted．

    I knew this would bother him deep inside．It would hurt his feelings and shut him up．

What I said filled him with anger．He tried to reach over my seat and grab me as he shouted．"That's it! That's it!"

    Surprised at his reaction，I sat back in seat．Never had I seen Nathaniel act like this before．

Later on，we were taken to the principal's office．

There，the principal told US to discuss the matter．It wasn't until then that I finally found that when I hurt someone physically，the wounds(伤口)eventually heal．But when I hurt them with my words，sometimes the pain never goes away．

    At the end of the discussion，I said sorry to Nathaniel．

    When I headed back to my room，I spent some time praying． I began to think about how often what I said hurt others．But I believe that as I keep praying and asking God to help me，he'll tell me when to keep my mouth closed．

    A river was running happily in the hill, the valley(山谷) and the field. Soon it was stopped by a huge rock and the river was a little afraid and worried what it could do.

    The rock said, "Hi, baby！Where are you going？"

    The river answered, "I'm going to the sea. My mother is waiting for me."

    The rock made fun of the river and said, "You're too young. Go back to the hill at once. You can't get there. Don't come back here again!"

    The river was surprised to hear that and said, "I can only go forwards(向前).There's no river that goes backwards(向后)!"

    The rock became angry and warned the river. "Don't speak! If you don't go back, you will have to change your direction. Don't want to run over my body!"

    The river asked helplessly, "Where should I go？"

    "You can go anywhere you like. Just don't come close to me!"

    While they are talking, more and more water came here. Then it began to get out of control. The river ran quickly over the rock and the rock was washed pitifully.

    The river said proudly, "A weak person will change his goal and direction. A person who is strong will only go ahead and nothing can stop him!"

    There is an old man in a house. In the house there are many mice. The old man has a cat. Every day the cat catches the mice and eats them. One day, the old mouse says "All mice must come to my room this evening. We must find a way to deal with the cat." All the mice come. Many mice speak but they don't know what to do. At last a young mouse stands up and says "We must put a bell on the cat. When the cat comes near we can hear the bell and run away. So the cat can't catch us." "Who can put the bell on the cat" asks the old mouse. But no one answers.