In addition to winning the Nobel Prize in Physics for his accomplishme

OFFICIAL EXPLANATION

Concepts tested:
-- Both X and Y (idiom, correlative conjunction)
-- Usage of past perfect [HAD + verbED]
-- Correlative conjunctions and parallelism

• Split #1: the correct construction is Both X and Y

The idiom is strict; the second connecting word must be and.
Option A uses as well as rather than and.
Option B uses and also rather than and.

The phrases as well as and and also are not automatically wrong! See Notes.
Both phrases are wrong in this instance because they're messing up the idiom.
True, neither phrase is correct in very many official questions. But in both cases, a couple of official questions have used the phrases in correct answers.
Eliminate A and B

• Split #2: ON the Rogers Commission or simply the Rogers Commission?

X and Y must be parallel.

The non-underlined portion of the prompt commits us to not using on before the Rogers Commission.
"On" precedes the parallelism marker "both."
→ Because ON is placed before the word both, which marks the beginning of the idiomatic construction, ON applies to both X and Y in Both X and Y.
The word "on" must be "once outside or twice inside." See Notes, below.
Options B and C erroneously repeat the word on before the Rogers Commission.
Eliminate C (option B is already gone)

• Split #3: simple past tense (investigated) vs. past perfect (had investigated)

We use past perfect [had + past participle/verbED] to talk about "the past of the past."
That is, we use past perfect to show that one of two past events occurred earlier in time.
Option D uses had investigated for no reason.
We have no idea whether the Rogers Commission preceded the Manhattan Project and thus no reason to use past perfect.
(Well, we kinda do know. I sincerely hope that people know that the Manhattan Project operated during WWII, 45 years before the Rogers Commission.)
At the least, we have no reason to use past perfect.
Eliminate D

The correct answer is E.

• NOTES

The phrases and also and as well as are not automatically wrong, although they are not often correct.
Do not eliminate an answer simply because it contains and also or as well as.
Context matters. In this instance, the phrases are messing up an idiom.

• the words and also are NOT automatically wrong.
-- in this instance, and also is wrong because it changes the idiom, not because "and also" is always wrong
-- and also can be used for emphasis—but not when and also messes up an idiomatic construction
-- SPOILER ALERT: In this official question, here the phrase and also is in the correct answer.

• the words as well as are not automatically wrong
At the moment, I can't find the two official questions in which "as well as" is correct. (I'll look. I'm having a brain freeze.)

One official question contains a list of items and uses as well as to "tack on" another item, and the use of as well as signals that the final item is slightly different from or less important than the other list items. See this post by Mike McGarrry.
The other official question uses as well as to test whether you know about additive phrases that do not change the plurality of the subject.
→ The CEO, as well as her husband, is a Princeton graduate.
As well as is an additive phrase that does not affect the subject "the CEO." The verb is singular.

• Once outside, twice inside

I'm going to keep drilling this concept because GMAC keeps testing correlative conjunctions and parallelism.
What do I mean by "outside"?
I'll use square brackets to show the "boundaries" of the construction, this way:
[Both X and Y]
[Both the Manhattan Project and on the Rogers Commission]

ON comes before the word both.
ON is thus "outside" the construction one time. That placement is correct. We should not add another "on."
Correct, once outside: He was comfortable on || both a ski slope and a sailboat. ||
Correct, twice inside: He was comfortable || both on a ski slope and on a sailboat. ||
Wrong, once inside and once outside: He was comfortable on || both a ski slope and on a sailboat. ||

COMMENTS

Nice work, both of you.
shameekv1989 , I am bumping you to best community reply.
Happy kudos.