We understand _______small changes to our land can have a big impact upon our environment __________ as we know is vulnerable enough.
A.what; which
B.what; where
C.how; where
D.how; which
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A解析考查固定句式以及定语从句。因为small changes是名词短语，所以用what引导。第二空是考查定语从句。As we know 是插入语，可以省略，which指代先行词environment在句中做主语。句意：我们理解，对土地的小小的改变可能会对很脆弱的环境有很大的影响。