How will the right answer fit in terms of support and conclusion?

Only the right answer will be support that doesn’t bring in anything new. That pretty much always works, although it’s technically more precise to say only the right answer must be true if the conclusion is true.

Highlight the main conclusion in the passage, if there is one:

most of the nations stating that their oil reserves were unchanged are probably incorrect.

[BACKGROUND]. But [SUPPORT]. Therefore, [INTERMEDIATE CONCLUSION]. So [MAIN CONCLUSION].

Map the wording of the answers to the wording of the passage:

(A) For any nation with oil reserves….

Stop. The argument is only about “nations stating that their oil reserves were unchanged”. No other nations are mentioned. So there couldn’t be anything about “any nation with oil reserves” that must be true based on the conclusion.

(B) It is likely that in 1997, in most of the nations that stated…

Notice how this answer specifically sets the exact same context as the passage. We likes. And all the wording in this answer matches wording used by the author. It doesn’t bring in anything new or use stronger terms than the argument used.

And, if the conclusion is true and most of these countries are “probably incorrect”, then it’s definitely “likely” that their oil reserves went up or down in the way the author described.

(C) …not only gradually dropped but also rose suddenly.

This is tricky, but the author never said oil reserves had to drop and rise. It could totally be just one or the other. So no way this info has to be true to make the conclusion work.

(D) …that nation drained its old oil fields and discovered new ones.

Same as (C), there’s nothing in the passage telling us both of these things had to happen in the same country.

(E) …that nation is obligated to report the change correctly.

The author didn’t say anything about anybody being “obligated” to do anything. No way this has to be true based on the conclusion.

(B) is the correct answer.