问题描述：
Earth is a target in a cosmic shooting gallery,subject to random violent events that were unsuspected a few decade ago.
我选的是 Since most violent events on Earth occur randomly,nobody can predict when or where they will happen.
Until recently,nobody realized that Earth is exposed to unpredictable violent impacts from space
我选的是 Since most violent events on Earth occur randomly,nobody can predict when or where they will happen.
Until recently,nobody realized that Earth is exposed to unpredictable violent impacts from space
问题解答：
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