GMAT Sentence Correction (SC) | Re: If Vs Whether

I learned this from somewhere - to test whether usage of 'if' is correct, do a simple test.
Flip the sentence to a format of 'If..then..' statement - it it makes sense, it will be the right answer..

for example:
This decade has seen no end to the controversy over if state-run day care centers are a necessary response to changes in employment patterns

Inverting to 'if then' format looks like:
if state-run day care centers are a necessary response to changes in employment patterns[then] this decade
...

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