下列各组物质中，前者属于混合物，后者属于氧化物的是（）

    I was sitting in the far back in a pizza house when I noticed the man, about thirty years old, carrying a pizza box. He sat down at the table to my right and then 1 his large dirty paper bag of clothing down on the floor. Obviously, this man was homeless and 2 a bath. He picked up the one small slice（薄片）of pizza and very slowly, very carefully, he began to eat, taking very little 3.

    He finally finished his meal and did something that I would never 4. He turned the box on its corner and slid the few5bits into one corner. Then he 6 his index finger（食指）and tried to pick up the small bits.

    Oh, how much it hurt me once again to see myself 7 I was thirty years ago. No food, no 8, and no clean clothes. Most of my past life had always been 9 to that of the young man and it all came back to me 10. The muscles in my neck began to tighten and my eyes began to burn and water up. I coughed a bit, trying to clear my 11 and get myself back together.

    I got four large slices of pizza from the counter and sat them down on his table, saying, “I thought you 12 like to have a few slices.”

    I did not stop at all but walked around behind him. As I passed him, I reached out and13him on the back, just one time, very softly with my hand. I hope that man knows that someone, someplace,14 him as a human being. And I am so 15 that I have never forgotten what it feels like to be down, out, dirty and hungry.

根据短文理解，选择正确答案。

    In choosing a friend, one should be very careful. A good friend can help you study. You can have fun together and make each other happy. Sometimes you will meet fair­weather friends. They will be with you as long as you have money or luck，but when you are down, they will run away. How do I know when I have found a good friend? I look for certain qualities of character，especially understanding, honesty and reliability(信任)．

    Above all else, I look for understanding in a friend. A good friend tries to understand how another person is feeling. He is not quick to judge. Instead, he tries to learn from others. He puts himself in the other person's place, and he tries to think of ways to be helpful. He is also a good listener.

    At the same time, however, a good friend is honest. He does not look for faults in others. He notices their good points. In short, a friend will try to understand me and accept me.

    Another quality of a friend is reliability. I can always depend on a good friend. If he tells me he will meet me somewhere at a certain time, I can be sure that he will be there. If I need a favor，he will do his best to help me. If I am in trouble, he will not run away from me.

    There is a fourth quality that makes a friend special. A special friend is someone with whom we can have fun. We should enjoy our lives, and we would enjoy our friendship. That is why I especially like friends who are fun to be with. A good friend likes the same things I like. We share experience and learn from each other. A good friend has a good sense of humor too. He likes to laugh with me. That is how we share in the joy of being friends. And I know that he is looking for the same quality in me.

    When I meet someone who is reliable, honest, and understanding，I know I've found a friend!