Now there’s a system the waste is disposed of using the principles of ecology.
A. when
B. which
C. that
D. where
网友回答
A. when
B. which
C. that
(答案→)D. where
解析：句意：现在有个系统利用生态学原理处理废物。这句话用了定语从句，先行词是a system，定语从句中不缺主宾表，缺少的是地点状语in the system，所以用where引导定语从句，选D。