Great amounts of water            poured into the river from the factories two years ago.

was

were

has been

have been

考查时态和主谓一致。句意：两年前，工厂将大量废水排入河中。根据two years ago 可知，句子使用一般过去时。....amounts of修饰不可数名词作主语时，谓语动词用复数形式，即谓语动词与amounts保持数的一致。故选B项。

"Society" is a(n)              term;it may mean much or nothing.

autonomous

ambiguous

fragrant

fragile

考查形容词词义辨析。句意：“社会”是一个模棱两可的词；它可能意味着很多，也可能没有意义。autonmous 自治的；ambiguous模棱两可的；fragrant芳香的；fragile脆弱的。结合后文it may mean much or nothing可知，空格处填ambiguous模棱两可的。故选B项。

It is six months         the online class started.

that

until

before

since

考查固定句型。句意：在线课程已经开始六个月了。A. that 那，那个；B. until直到..... 为止；C. before在.....之前；D. since自.....以来。分析句子可知，句中涉及固定句型“ It is +一段时间+since引导的时间状语从句”，意为“自从......以来已经有多长时间了”，since从句中用非延续性动词。故选D项。