Explanation

Creating a filter: In the original sentence, the verb "had been" raises a flag. As we saw in Punctuated Equilibrium, the past perfect must refer to a past point before another past point. That may be the intended meaning here: it had rarely been captured (=further past) until recently (=recent past). Tentatively keeping choice (A) in, we can go to the answer choices.

Finding objective defects: at a glance, the answer choices fall into two groups, the "occurs" and the "appear." We are talking about something grammatically singular, "inversion," so "occurs" is correct and "appear" is incorrect.

That leaves us with (A) and (B), which differ only in the placement of the phrase "at the Grand Canyon." One of these two options must be objectively incorrect. Which conveys the intended meaning? Choice (B) seems to say that total cloud inversion only occurs once a decade period -- as in anywhere. We don't have to be a meteorologist to know that's probably not right: it's at the Grand Canyon that it occurs once a decade. The correct answer is (A).