陨石碰撞和恐龙灭绝 求助问题

sharon20UID: 3013082

Earth is a target in cosmic shooting gallery, subject to random violent events that were unsuspected a few decades ago .

同义句转换：

A.Until  recently ,nobody realized that Earth is exposed to unpredictable violent impacts from space.
B. In the last few years,the risk of a random violent impact from space has increased.
C.Since most  violent events on Earth occur randomly ,nobody can predict when or where they will happen.
D.A few decades ago,Earth became the target of random violent events originating in outer space.

这道题琢磨了蛮久，句子还是没懂，求助GTER 们 解答下，原句是什么意思，为什么选A  ，错误选项为什么错~谢谢各位了！！！

xpp927UID: 2205349

把原句主干拆分一下就是：……that were unsuspected a few decades ago. that指的就是前面的现象。理解了前后的意思，选A就清楚了呀。

sharon20UID: 3013082

I  got it  ,thank you !! 2# xpp927