The members of the Organization of Petroleum Exporting Countries usual

B. "its" is clear referent but not "their".
"designed to" is more idiomatic than "designed for".
"maximize" is better than "maximization of".

I will go with B, because subject is first of all is the word members, if we change the sentence slightly like this

The members ... usually comply with (their) decisions, which are designed to maximize the long term profits of member nations.

We will see that the end of the sentence (member nations) is clearly referring to OPEC. It will not make logical sense with the ending of the sentence if we put their decisions...
IMO B

i agree with B.
its point to org

D sounds bad.

A.their decisions, which are designed to maximize
OPEC is singular. So their is out.

B.its decisions, which are designed to maximize

C.their decisions that are designed for the maximization of
OPEC is singular. So their is out.

D.its decisions that are designed for the maximization of
Passive voice. Out.

E.its decisions, designed as they are to maximize
Sounds awkward.

Leaves B.

A.their decisions, which are designed to maximize>>>incorrect use of 'their' as organisation is singular
B.its decisions, which are designed to maximize >>perfect
C.their decisions that are designed for the maximization of>>wordy
D.its decisions that are designed for the maximization of>>wordy
E.its decisions, designed as they are to maximize>>wordy

Here the pronoun after Organisation .... refers to the organisation itself which btw stands for OPEC, so the correct pronoun should be:

The members of the Organization of Petroleum Exporting Countries usually comply with its decisions.... Cancelling options A and C. immediately.

E is seems awkward, so keep it aside.

Now remains B and D.

Look at the sentence and both options. the second part designed to maximize..etc etc is extra information.

D makes it sound as if the countries comply to only those decisions that maximize profits.
Does it seem so?

Leaving option B.

Finally

The members of the Organization of Petroleum Exporting Countries usually comply with its decisions, which are designed to maximize the long term profits of member nations.

A and B are both correct in my opinion.

How can we say that it's Organization's decisions that the members comply with. Why it could not be members' decisions that the members comply with. After all, the members' decisions are Organization's decisions.

good question...
I fell for A... very subtle difference between A and B... Normally its the companies decision that the employees follow(this includes all the employees)....

OPEC is the organization...So it has to be "its' instead of their....

It should be A. "of" here is just another middleman.

The members [strike]of the Organization of Petroleum Exporting Countries[/strike] usually comply with their decisions, and not its decisions

Please correct me if I am wrong

Go to this link and search for "members of the court". See that its followed by their and not it/its

https://en.wikipedia.org/wiki/Internatio ... of_Justice

B, members is the subject for comply.... and it's is the pronoun for the organization...

+1 B

Meaning is critical here. If we use "their", the decisions could not be related to the decisions taken in that organization.

", which" is better because, the new clause provides additional information about those decisions.

"The members" and "Petroleum Exporting Countries" have the same chance to be the antecedent of "their", so "their" is ambiguous. "its" is clearer, only one antecedent, organization.

Choice B is the correct one.

their refers to the organization and hence is incorrect. B is correct one.

its is d correct pronoun for Org of......, so eliminate A n C
which....... is a non essential modifier
i vote for B..

in D, it is not clear who make maximization so is wrong.
in b, the decisions maximize and is so correct and logic

honestly, I am afraid of choice d.

Debatable OA. The subject here is 'Employees' and not 'OPEC'. The noun within a prepositional phrase cannot be the main subject of the sentence. And also, because the original sentence says 'their', I think it is safe to with the Employee's decisions. Experts please correct me if i am wrong. GMATNinja GMATNinjaTwo BillyZ generis Abhi077