The book's explanation's explanation is often inadequate. I can only do so much here, but here's my 2 cents.

Many students have difficulty identifying which is the subject: "one" "a number of" or "industrialized nations"
We know "one" is singular. We know "a number of" is plural (NOT singular as someone mentioned). And of course the word following the phrase "a number of"--which in this case is "industrialized nations" will be plural.

so what do we use? singular or plural?

Well, the keyword here is "that"..By adding the word "that"..you are restricting the scope of industrialized nations you are referring to. You are not referring to ALL industrialized nations, but rather the ones THAT blah blah blah. Therefore, because of the word "that" you must use the plural form.

If the word "that" was not there, then you would use the singular form "is accepting"

But since we do have the word "that" and you are restricting the scope of industrialized nations that you are referring to, you must treat "a number of industrialized nations" as the subject, and use "are accepting"

That leaves us with C, D, and E. Of the three, only "their responsibility" makes sense in the context of "are accepting their responsibility"---you can eliminate C and D. The answer is E.

Again, I can only explain so much in text. This question falls into framework #7 of the GMAT Pill Study Method.
_________________

... and more


Zeke Lee, GMAT Pill Study Method (Study Less. Score More.) | Download Ebook
- How A McKinsey Analyst Struggled with GMAT for 2 Yrs
- GMAT Score From 650 to 760 + 25 Minutes left on the exam! Wow!

GMAT Pill Reviews

just curious...

when the answer choices consist of a 2/3 split such as this SC problem's answer choices does, how often is the correct answer between the 2 or among the 3? Has any one seen any data regarding this?

Thanks GMATPill instructor! Your post was really helpful. Just to add my 2 cents: I was really confused as to what is the subject of the sentence. I had thought it was "Sweden" but according to the OA (E) it seemed that "a number of industrial nations" should be the subject instead. (FYI "A number of" is plural vs "The number of" which is singular)

For me, the key to understanding the question was breaking the sentence into 2 parts. The first part is "Sweden is (but) one of a number of industrial nations". Here, the subject is "Sweden" which agrees with the singular verb "is". The second part is "a number of industrial nations that..." The word "that" introduces a relative clause which modifies "a number of industrial nations". Hence, the verb/ pronoun in the relative clause should agree with "a number of industrial nations", and be plural ("are"/ "their") Hope this helps anyone who was as confused as I was!