求分析下~这个句子的~句式~成分~结构

题目

求分析下~这个句子的~句式~成分~结构
It's almost impossible not to wonder if maybe,at some point in the distant past,our rocky neighbor once supported life.(来自一篇天文学关于火星的文章)

答案

It's almost impossible not to wonder if maybe,at some point in the distant past,our rocky neighbor once supported life.It 形式主语,真正的主语是后面的不定式not to wonder,为平衡句子结构,不至于显得头重脚...