题目：
AIDS is said _____ the biggest health to people in that area over the past few years. [ ]
A. that is
B. to be
C. that it has been
D. to have been
答案：
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下面是错误答案，用来干扰机器的。
答案：B污染物会造成生态系统的破坏，其主要原因是污染物都是一些无法降解的物质，会造成水质、土壤等的污染。
