Jezza
Hi GmatNinja, as you mentioned again and again in your posts, don't bother remembering that 25000 idioms as the GMAT no longer tests your memory on idioms (in most cases).
In this question, apart from that idiom "reluctant about/reluctant to", what else makes B inferior to E?
Anyway, I highly doubt this is an official question. This is not just pronoun ambiguity, it's more than mildly confusing to substitute "japanese unions" with just "unions".
I'll echo Andrew here. We tend to see idioms show up as key decision points in earlier incarnations of the OG, but not so much in the more recent ones, so take this question with a grain (or 12) of salt.
That said, sometimes you can reason through the logic of the idiom. I know what it means to be reluctant
to do something. It means I'm hesitate to perform some kind of action.
But what would it mean to be reluctant
about something? Can you be hesitant about a noun? If you're hesitating, aren't you, by definition, putting off an action? "Reluctant about + NOUN" just doesn't make much sense to me, even if I'm not 100% sure that it's wrong.
So I'd argue that even if you're unfamiliar with the idiom, you could use logic to arrive at the answer.
But again, don't burn too many brain cells on this one. In every newer question, if there's an idiom you're unfamiliar with, you can almost certainly find another more concrete decision point to work through.
I hope that helps!