新东方蓝皮书语法求解 SECTION5-Q4

Serena11457

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.
(A) an especially serious pollutant because it diminishes the respiratory system’s ability to deal
(B) an especially serious pollutant because of diminishing the respiratory system’s capability of dealing
(C) an especially serious pollutant because it diminishes the capability of the respiratory system in dealing
(D) a specially serious pollutant because it diminishes the capability of the respiratory system to deal
(E) a specially serious pollutant because of diminishing the respiratory system’s ability to deal

答案选A，我选C。
不是说必须是有生命的人才可以用's格式所有格吗？ system's ability也是对的？