Hello Grammar Exchange members!
(a) Only when he needed some help did he call me.
(b) Only if we invest more money can we save the company.
I'd like to ask you whether or not the dependent clauses in (a) and (b) can be reduced.
To the best of my knowledge "Only when he needed some help" can be reduced to "Only when needing some help" as in (c) because the subject in the dependent clause is the same as the subject in the main clause.
(c) Only when needing some help did he call me.
However, I only see the change when the conjunctions leading the dependent clauses are when, while, after, before, etc.
So the question I have here is what about if in (b)?
(d) Only if investing more money can we save the company.
Is (d) possible?
Thanks in advance!