请问，下面这句话应该怎么理解？make在这里是什么用法

句子的主干是： It is impossible. it 是形式主语，真正的主语是后面的to make more than the wildest guess at how many they kill
正常的语序应该是to make more than the wildest guess at how many they kill is impossible。但是这样会显得头重脚轻 所以用it放句首来暂时代替 后边这个不定式主语。
guess at st