My question here is related to 'the bears'. In many other cases when nouns are used with prepositions, this is translated into English with a definite article while the Romanian nouns do not have the definite form. In this case, using the observation explained above, it would be logical to expect indefinite bears. However, we see 'ursii' after all. How can this be anticipated, especially in the auditing exercise, and how this issue of prepositions and definite/indefinite nouns should be addressed in Romanian altogether?
You're right, most prepositions are followed by a noun without a definite article in Romanian. "Cu" is the only exception where a stand alone noun can have a definite article after. Also, if the noun following the preposition is modified, it takes a definite article. For instance, if you want to say, "We are running away from the black bears", you would say in Romanian, "Fugim de urșii negri". I hope that helps...
Cu plăcere! ;) "la" isn't an exception to this rule either. A good example is when you're answering the question "Unde ești?" You could reply with something like "La magazin", but not "La magazinul". The latter just sounds awkward... Feel free to report it if the noun has an article without being modified.
It can also mean "at the same time".
Here, it is synonymous with "deodată", which you could use if you wish to avoid confusion (although their very similar forms and the fact that "deodată" could also mean "suddenly" might be even more confusing...).
Another alternative is "în același timp" which is closer to the English form.