I emailed ETS, and they responded. Here's a receipt of the correspondence.My email:
Here is the pertinent information:
Test Center: [-]
Test Date: October 29th, 2016
Test Name: GRE Physics Test
Question Number: I don't remember exactly - somewhere in the middle
Question Content: The question was the following:
About half of all elements heavier than iron in the universe originated from:
(A) The big bang
(B) Nuclear fusion in main sequence stars
(C) Nuclear fission in main sequence stars
(D) Nuclear fission in asymptotic giant branch stars
(E) Neutron capture in supernovae explosions
I don't think any of these answer choices are correct. About half of elements heavier than iron come from the s-process in asymptotic giant branch (AGB) stars , and half come from the r-process. But the dominant site for the r-process is unknown! It was believed for a long time that the dominant site was core-collapse supernovae , but with recent observations of black-hole mergers  and intensive neutron star calculations  this belief has been skewed.
So, in summary, I believe the intended answer was (E), neutron capture in supernovae explosions, but anybody who works in nuclear astrophysics knows that that is not so simply true. In fact, it may be completely false. I've conducted research on nuclear reactions pertinent to the s-process in AGB stars, so I was aware of the complications of this question. I was quite confused when I came across this question, and ended up choosing choice (D) because I figured that maybe it was intended to say "Neutron capture in asymptotic giant branch stars".
 http://iopscience.iop.org/article/10.10 ... 012021/pdf
 http://iopscience.iop.org/article/10.10 ... .text.html
 http://journals.aps.org/prl/pdf/10.1103 ... 116.241103
 http://journals.aps.org/prc/pdf/10.1103 ... .92.055805
"Your inquiry regarding a question on the Graduate Record Examinations (GRE) Physics Test that was administered on October 29, 2016 was reviewed by the ETS assessment specialists responsible for the test, as well as by the external GRE Physics Committee of Examiners.
The question is concerned with the production of elements heavier than iron. Your inquiry indicates that you believe that none of the answer choices are correct. Upon reviewing the question, we have determined that the question (including answer choices) is worded correctly in the test book and has a single best answer listed among the answer choices presented. Your e-mail mis-states the problem as: "About half of all elements heavier than iron in the universe originated from ...", which is significantly different from the actual wording in the test book. Also, the papers that you cite either tend to support, rather than refute or contradict, the correct answer to the question or are not relevant to what is actually being asked. Unfortunately, the question cannot be discussed in more detail, because it has not been made public.
Thank you for taking the time to bring your concerns to the attention of ETS. ETS makes every effort to ensure the accuracy of all its tests and is always looking to improve them."