求助一道语法题

依然雏田

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.  
 an especially serious pollutant because it diminishes the respiratory system's ability to deal  
 
 an especially serious pollutant because of diminishing the respiratory system's capability of dealing  
 
 an especially serious pollutant because it diminishes the capability of  the respiratory system in dealing  
 
 a specially serious pollutant because it diminishes the capability of  the respiratory system to deal  
 
 a specially serious pollutant because of diminishing the respiratory system's ability to deal

弗拉多

especially表示严重性
specially表示特别的

这里根据句意应该是especially
BC里面，capability of doing结构被ETS认定为awkward