請問這句and had they not felt so sorry for the poor Scarecrow they could havebeenveryhappy.為什麼had放在they前面?又不是問句?謝謝?

From the book called"The Wizard of Oz":-
The conditional:-
NB:-felt sorry must be changed to had told;
------could have been must be changed to would have been.
------very happy must be changed to more happy.
------Conditional adj, depending on a certain condition eg:-Their agreement to make the Scarecrow happy "were conditional" on their telling him all the story.---------------------->In the conditional for the "If Clause":-If they had told the Scarecrow"Main Clause":-they would not have been felt so sorry.To be rewritten as:-Had they told the Scarecrow, they would have been more happy.===>Had they not felt so sorry for the poor Scarecrow;=Had they told the Scarecrow;====>they would have been more happy=they could have been very happy=they would have been more happy.