Neal, these are not grammatical terms but the meanig of the pronoun 'некоторый'. I will try to give an examples. а) О его раздражительном характере можно судить по некоторым его поступкам. б) Он произнес эти слова с некоторым смущением. в) За год он наблюдал некоторый прирост значения ВВП. It was hard for me too )

Thanks KP for all the thoughts/responses. At least I know have a better sense of what the exercise is about. It was really baffling at first. It is interesting to me how many native speakers have said how difficult this exercise it. I'll be sure to convey that sentiment to my teacher this morning at my lesson :-)

I think what he means now is merely "can be substituted with отдельный in this or similar context". Ok. There are clichés like "несмотря на отдельные недостатки" and "некоторые недостатки". They mean different things ))))), but I don't see how ANY of other ways to use "отдельный" can be confused with 'некоторый'. Отдельный always refers to discrete units. "отдельные ХХХ" is always a subset of discrete units. So I know where we can NOT use отдельный. But отдельный means:

(If it is not clear from the beginning... I'm just thinking aloud, in case it may be helpful:-) So I continue...) Nevertheless, I believe, the author implied 'insignificant' as the correct answer for 18. Because he added this "but". And because the word "незначительный" isn't normally used with 'смущение', for example. Now I'll try to discriminate "отдельный" and "неопределенный". I think by "отдельный" he doesn't mean 'separate' which is the literal meaning of 'отдельный' besides a bunch of idiomatic meanings.

At this place I stuck for a while. Interpretation as "неопределённый" (unspecified, vague) is also possible!!! Moreover, I even feel that it DOES mean 'неопределенный" here!! I can also analyze the last phrase as "certain interest.... BUT rather insignificant interest". I can though offer the following argment for the author's interpretation: a similar phrase with "незначительный интерес" can be constructed and feels natural. So possibly these two clichés could interact in the mind of whoever uttered this newspaper-styled phrase.