CR : Assumption. Need help with negation

[desiwolverine]

A newborn kangaroo, or joey, is born after a short gestation period of only 39 days. At this stage, the joey's hind limbs are not well developed, but its forelimbs are well developed, so that it can can climb from the cloaca into its mother's pouch for further development. The recent discovery that ancient marsupial lions were also born with only their forelimbs developed supports the hypothesis that newborn marsupial lions must also have needed to climb into their mothers' pouches.

The argument in this passage relies on which of the following assumptions?

(A) All animals that are born after a short gestation period are born with some parts of their bodies underdeveloped.
(B) Well developed forelimbs would have been more advantageous to ancient marsupial lions than well developed hind limbs would have been.
(C) If the newborn marsupial lion did not climb into its mother's pouch, then paleontologists would be able to find evidence of this fact.
(D) Newborn marsupial lions that crawled into their mothers' pouches could not have done so had they not had only their forelimbs developed at birth
(E) Newborn marsupial lions would not have had only their forelegs developed if this development were of no use to the marsupial lions


In the problem above , I was stuck between choice D and E.
Between D and E , I decided to negate to see which ans choice when negated destroys the argument(conclusion).

Negation of choice E :
Newborn ....... would have had only their forelegs developed if ............. were of no use to the marsupial lions.

Negation of choice D :
Newborn ......... could have done so if they had only their ..... at birth.

I wanted to check if I am negating the choices correctly.

THanks

[tim]

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