There are some warnings in some countries over exploitation of underground water has caused the decline of wetland and increase of desertification.
A. which
B. where
C. what
D. that
网友回答
A. which
B. where
C. what
(答案→)D. that
解析：考查同位语从句：句意：在一些国家有很多警告，过分的开采地下水已经导致湿地的减少和沙漠化的增加。这里横线后面是同位语，说明warnings的内容，因为同位语从句的成分和意思都是完整的，用that连接，that不做成分，只起到连接的作用，但是也不能省略，which哪个，where哪里，what什么，不符合句意，选D。