【正确答案】但更为重要的是，这是科学家们所能观测到的最遥远的过去的景象，因为他们看到的是150亿年前宇宙云的形状和结构。

【答案解析】[精解] But even more important，it was the farthest that scientists had been able to look into the past，for what they were seeing were the patterns and structures that existed 15 billion years ago．
句子分析：
一、句子可以拆分为三段：But even more important，it was the farthest that scientists had been able to look into the past，/for what they were seeing were the patterns and structures/that existed 15 billion years ago．
二、句子主干结构是：主句+for+原因状语从句。
1)主句是强调句让was．．．that．．．被强调部分the farthest 是后面句子的状语，可以理解为 scientists had been able to look the farthest into the past。
2)for．．．引导的原因状语从句是一个系表结构，what they were seeing 是从句中的主语， that…是名词表语the patterns and structures 的定语从句。
三、词的处理：
even more important (省略)更为重要的是；
the patterns and structures (宇宙云的)形状和结构；
15 billion years ago 150亿年前；