Since the controller WANTED (past) to known, then I would say "had checked." I think "left" is okay, although "had left" also works. I'm surprised the answer key identifies "left" as the problem and not "had checked over."
I've changed my opinion on this one a couple of times. "had left" is without doubt the better option, because the use of past perfect indicates that the report was left on the desk prior to the controller asking the question. Since both are past actions, past perfect is used to frame them in time and put one before the other.
Regarding "checked over" or "had checked over": Hmmm -I'
Sorry that I had to I repost this question because the previous one was locked and some imortant contents have been deleted. I am still confused after seeing the rest of the advice left. Appreciate your help!!
Sorry, if the comments haven't been that helpful. I think the best way to think of it is that "had left" and "had checked over" are probably best supported by the 'commonly held' rules of grammar. However, since reported speech is most often heard in conversation rather than in written form, grammatical rules are frequently applied much more loosely, especially by native speak
Thank you Saiing. I think learning a language is a pleasant thing. We may've been paying too much attention to grammar issue because the tests we took required us to do so. Actually learning how to speak is the first thinig first after all. Thanks for help.