A) What allow us to get off the ground are studying, practicing, and asking for help.
B) It is studying, practicing, and asking for help what allow us to get off the ground.
These are excerpted from a local grammar book, on which the author says, A) (wh-cleft sentence) can be converted into B) (extraposed construction).
I wonder if a fused relative clause could be extraposed. In relation with this inquiry, I found following references;
1. ‘No extraposition’ (CaGEL by Huddleston, p.1069)
C) a) ‘What she suggests is unreasonable.’
b) *It is unreasonable what she suggests. (ungrammatical)
Like ordinary NPs, fused relatives do not occur in the extraposition construction.
2. ‘Extraposition of a clausal subject’ (CoGEL by Quirk, p.1392)
But it is worth emphasizing that for clausal subjects (though cf 18.34) the postponed position is more usual than the canonical position before the verb (cf 10.26). Examples are:
D) Type SV: It doesn't matter what you do.
3. 446. preparatory it (1): subject (Practical English Usage by Swan - 3rd edition),
E) p.423, It doesn't interest me what you think.
F) p.424, George made it clear what he wanted.
(Personally I think these ‘what’ in D), E), F) is all fused relatives.)
While CaGEL says ‘no extraposition with fused relative – what’, CoGEL and PEU provide the references which might be understood to be ’extraposition allowed with fused relative’. Thus, I’m confused and really would appreciate if you kindly share your opinions for my two questions below;
1) If a fused relative clause could be extraposed or not?
2) If B) above is grammatically correct or not?