I always avoid going on field investigations with the toxics  team, unless it's  ly necessary. It's not that I mind the hard work, or am afraid of coming into contact with toxic substances. What I fear is quickly losing hope about the work I do.     However, doing field research with the toxic team, all I see and feel is filth---nothing else. Even if I close my eyes, I can smell the smell of food processing, rotting organic waste from paper mills and chemicals from clothing manufacturers.     One morning, I went to investigate a discharged pipe to document and collect samples of pollutants secretly being emitted by a textile mill. I had to work with the utmost secrecy in order to avoid being discovered by the textile mill.     I dipped a long measuring pole into the large polluting pipe to measure the volume of polluted water being emitted. But the surface of the water, covered in oil and filth, made me feel as if to vomit .     All of a sudden, I felt someone hit me on my back, it frightened me so much that I almost fell into the water. I grasped the pole and looked behind me to see an old man standing there. He asked: "Can you catch fish here?" I realized that he thought I was holding a fish pole, so I kept calm and said: "Yes, I heard that there's a kind of small fish living in this water, and it has medicinal benefits."     The old man grew quite curious and replied: "That may be. If a fish can survive in water as dirty as this, it must have a lot of resistance. So it wouldn't be too strange if such fish had medicinal benefits."     It was clear he was just passing by, so I answered: "Yeah, survival of the fittest. Fish that adapt can survive, just like us humans."     He kept talking to me and didn't want to leave. He wanted to see whether or not I would catch the small fish with medicinal benefits. The text is mainly about   _  .
a research report about pollution. an exciting experience of fishing. an experience of doing research on pollution an unforgettable talk with an old man.
Question: I always avoid going on field investigations with the toxics  team, unless it's  ly necessary. It's not that I mind the hard work, or am afraid of coming into contact with toxic substances. What I fear is quickly losing hope about the work I do.     However, doing field research with the toxic team, all I see and feel is filth---nothing else. Even if I close my eyes, I can smell the smell of food processing, rotting organic waste from paper mills and chemicals from clothing manufacturers.     One morning, I went to investigate a discharged pipe to document and collect samples of pollutants secretly being emitted by a textile mill. I had to work with the utmost secrecy in order to avoid being discovered by the textile mill.     I dipped a long measuring pole into the large polluting pipe to measure the volume of polluted water being emitted. But the surface of the water, covered in oil and filth, made me feel as if to vomit .     All of a sudden, I felt someone hit me on my back, it frightened me so much that I almost fell into the water. I grasped the pole and looked behind me to see an old man standing there. He asked: "Can you catch fish here?" I realized that he thought I was holding a fish pole, so I kept calm and said: "Yes, I heard that there's a kind of small fish living in this water, and it has medicinal benefits."     The old man grew quite curious and replied: "That may be. If a fish can survive in water as dirty as this, it must have a lot of resistance. So it wouldn't be too strange if such fish had medicinal benefits."     It was clear he was just passing by, so I answered: "Yeah, survival of the fittest. Fish that adapt can survive, just like us humans."     He kept talking to me and didn't want to leave. He wanted to see whether or not I would catch the small fish with medicinal benefits. The text is mainly about   _  .
A. a research report about pollution.
B. an exciting experience of fishing.
C. an experience of doing research on pollution
D. an unforgettable talk with an old man.
Answer: