英语语法问题The reason these two wonders of nature are so difficul

这个不是同位语从句,而是定语从句,这里的the reason做explain的宾语,还原的话,这个句子应该是这样的these two wonders of nature are so difficult for many adults to explain the reason to children is that they are not very well understood by adults themselves.其实这个句子简单的看的话应该这样The reason is that they are not very well understood by adults themselves.
而reason后面的那一长串只是做定语,修饰the reason.其实这里的the reason后面应该有一个that的,但是由于the reason在定语从句中做宾语,that可以省略.
另外,同位语从句和定语从句的区别在于,在定语从句中连接词要做成分,而在同位语从句中连接词不做成分,只起连接作用.

是定语吧，省略了THAT
这句子包含一个定语从句，和一个宾语从句
……的原因是……