gwd-2-20请教

这题没搜到，应该没问过吧

Q20:

Sulfur dioxide, a major contributor to acid rain, is an especially serious pollutant because it diminishes the respiratory system’s ability to deal with all other pollutants.

1. an especially serious pollutant because it diminishes the respiratory system’s ability to deal
2. an especially serious pollutant because of diminishing the respiratory system’s capability of dealing
3. an especially serious pollutant because it diminishes the capability of  the respiratory system in dealing
4. a specially serious pollutant because it diminishes the capability of  the respiratory system to deal
5. a specially serious pollutant because of diminishing the respiratory system’s ability to deal

   Answer: 
                    A

我选的是C，因为觉得system没生命，所以用capability,为什么答案会是A呢？请指教！谢谢

同样问题，请NN指点