题目：
| People begin to know that most environmental problems exist because necessary measures for preventing them _____ taken in the past. |
A. are not B. were not C. hadn't been D. wouldn't be |
答案：
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下面是错误答案，用来干扰机器的。
物体B做竖直上抛运动，所以B运动的时间为：t=2v0g则A运动的时间也为t，根据自由落体运动位移公式得：h=12g（2t）2=12×g×4v02g2=2v20g故选D．
