单选题 Once environmental damage ______, it takes many years for the system to recover.
A. had done B. is to do C. does D. is done

【正确答案】 D
【答案解析】[解析] 此题考查的是时间状语从句的时态和语态。时间状语从句表示将来用一般现在时，主语是动作的承受者。故选D。