guys i have a quick q

consider this sentence (slightly modified to suit my question, so its not the same as in other posts)

It has traditionally been thought that all biological functions decline with age, but according to the National Institute on Aging, certain important capabilites, such as the output of the heart under stress remain essentially unchanged.

(a) output of the heart under stress remain essentially unchanged
(b) heart's output under stress remain essentially unchanged

is there a difference between the two sentences in GMAT terms?

I don't think there is a GMAT-term difference , however the possessive noun usage ('s) can only act as antecedent to possessive pronouns(its). If you use 's usage you cannot use something like

heart's output under stress remain essentially unchanged as it is a vital organ. =e> it cannot refer to heart

I dont see any change in both of these options.
Since they follow such as, it is termed as an example or citation in GMAT terms and there no use of relative pronouns in that clause also.

But shouldn't it be under stress remain[b]s[/b] unchanged... in both the options.

Output is a singular term rite.
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Aiming for 700+

Kudo me if the post is worth it

See the OG problem-
135. Spanning more than 50 years, Friedrich Müller
began his career in an unpromising apprenticeship
as a Sanskrit scholar and culminated in virtually
every honor that European governments and
learned societies could bestow.
(A) Müller began his career in an unpromising
apprenticeship as
(B) Müller’s career began in an unpromising
apprenticeship as
(C) Müller’s career began with the unpromising
apprenticeship of being
(D) Müller had begun his career with the
unpromising apprenticeship of being
(E) the career of Müller has begun with an
unpromising apprenticeship of
Logical predication; Idiom
What spanned more than 50 years? It was
Müller’s career that spanned 50 years and
culminated in virtually every honor. Th e correct
subject of the sentence must be Müller’s career.
A Müller’s career, not Müller, should be the
subject of the sentence.
B Correct. Using Müller’s career as the subject
of the sentence solves the modification
problem with spanning … and provides a
logical subject for culminated.
C Apprenticeship of being is an incorrect idiom;
apprenticeship as is correct.
D Müller’s career, not Müller, should be the
subject of the sentence; past perfect tense is
inappropriate; apprenticeship of being is an
incorrect idiom.
E Müller’s career is preferable to the career of
Müller; present perfect tense is incorrect;
apprenticeship of should be apprenticeship as.
_________________

* An ounce of prevention is worth a pound of cure
** Every single second counts.
*** One KUDO earned is One step closer to GMAT. Help me in getting closer to GMAT.
**** i-invite-you-in-my-gmat-journey-121396.html.


Test Description_______Date____Total___Quant_____ Verbal
GMAT PREP1_____________________610
GMAX online test 1____29.07.2011__540_____43________19
MGMAT CAT 1_________03.09.2011__580____42________28
MGMAT CAT 2_________02.10.2011__690____48________36
GMAX online test 2_____16.10.2011__640____48________32
MGMAT CAT 3_________23.11.2011__670____47________34
Veritas free CAT______ 31.10.2011___630___ 46________33
MGMAT CAT 4_________06.11.2011__690____48________36
MGMAT CAT 5_________13.11.2011__660____46________34
MGMAT CAT 6_________19.11.2011__680____51________33
GMAT PREP2__________23.11.2011__680
GMAT Exam___________24.11.2011__690____50________34

I don't know if it is very useful, but you can check option "E".

E Müller’s career is preferable to the career of
Müller; present perfect tense is incorrect;
apprenticeship of should be apprenticeship as.
_________________

* An ounce of prevention is worth a pound of cure
** Every single second counts.
*** One KUDO earned is One step closer to GMAT. Help me in getting closer to GMAT.
**** i-invite-you-in-my-gmat-journey-121396.html.


Test Description_______Date____Total___Quant_____ Verbal
GMAT PREP1_____________________610
GMAX online test 1____29.07.2011__540_____43________19
MGMAT CAT 1_________03.09.2011__580____42________28
MGMAT CAT 2_________02.10.2011__690____48________36
GMAX online test 2_____16.10.2011__640____48________32
MGMAT CAT 3_________23.11.2011__670____47________34
Veritas free CAT______ 31.10.2011___630___ 46________33
MGMAT CAT 4_________06.11.2011__690____48________36
MGMAT CAT 5_________13.11.2011__660____46________34
MGMAT CAT 6_________19.11.2011__680____51________33
GMAT PREP2__________23.11.2011__680
GMAT Exam___________24.11.2011__690____50________34