【题目】People are recycling many things which they away in the past.
A.had thrown
B.will be throwing
C.were throwing
D.would have thrown

【答案】D
【解析】句意：人们现在正在回收过去会扔掉的东西。这句话的which引导的是定语从句，是一个隐含的虚拟语气，因为in the past相当于If they had been in the past，所以句子用虚拟语气，和过去相反用would have done。所以选D。