It is impossible to make more than the wildest guess at how

他们屠杀了多少（动物）是很难做出更多的胡乱猜测的。wild guess胡乱猜测,the wildest guess最胡乱地猜测。此句由动词不定式to make more than the wildest guess at how many they kill。做主语,由it做形式主语,is impossible系表结构；其中主语从句中：make guess at做谓语,how many引导宾语从句。