例 But science does provide us with the best guide to the future, and it is critical that our nation and the world base important policies on the best judgments that science can provide concerning the future consequences of present actions.
“It+ is/was + 被强调的部分+ that/who…+剩余部分”
Tom bought a book yesterday.
It was a book that Tom bought yesterday
It was Tom that bought a book yesterday
形式主语：It is a good thing that he goes to school.
3. 强调句子：hence, above all, in the world, on earth
(1) His project has turned out to be lots of puzzlement about what in the world those readers really want.(2001年Text3)
(2) By the third generation, the original language is lost in the majority of immigrant families.” Hence the description of America as a “graveyard” for language.(2006年Text1)