___is known to us all that the old scientist,for ___ life was hard in the past,still works hard in his eighties.
___is known to us all （注意这里）is that the old scientist,for ___ life was hard in the past,still works very hard in his eighties.
你的题没那个is
你的是It is konwn to all that
他的是What is known to all is that
It is konwn to all that=What is known to all is that