og上一道省略的题，搞不清怎么省略

richygogogo

Digging in sediments in northern China, evidence has been gathered by scientists suggesting that complex life-forms emerged much earlier than they had previously thought.

　　(A) evidence has been gathered by scientists suggesting that complex life-forms emerged much earlier than they had

　　(B) evidence gathered by scientists suggests a much earlier emergence of complex life-forms than had been

　　(C) scientists have gathered evidence suggesting that complex life-forms emerged much earlier than

　　(D) scientists have gathered evidence that suggests a much earlier emergence of complex life-forms than that which was

　　(E) scientists have gathered evidence which suggests a much earlier emergence of complex life-forms than that

这道题的C选项代入：Digging in sediments in northern China,scientists have gathered evidence suggesting that complex life-forms emerged much earlier than previously thought.这种省略有什么规律吗？可以把scientists省略吗？