A newborn kangaroo, or joey, is born after a short gestation

IMO D is the correct answwer... :confused!

could anyone please explain the answer further? how do i eliminate other choices here?

The answer is E; visit the following link for an explanation:
https://www.f1gmat.com/newborn-kangaroo-or-joey

I'm still confused between D and E and D sounds only better of the two to me for the reason below:

E would’ve sounded better if it was slightly different:

[E] Newborn marsupial lions would not have had only their forelimbs developed if this development were *not for climbing to the lion’s pouch* instead of “of no use to the marsupial lions.”
or had this option been like the one below:
[E] Development of the forelimbs is NOT/NEVER for any other purpose.
I rejected option E with an understanding that it is too extreme to say “of no use to M. lions”. They could’ve had developed forelimbs for some other purpose. So, the person arguing must think that “development of forelimbs” is NOT for any OTHER purpose i.e. is for the SOLE purpose of climbing to the pouch.

(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.

D is also a weak statement for an assumption since it says “they couldn’t have crawled to the pouches if they didn’t have developed forelimbs” –> this doesn’t necessarily mean that they did use their forelimbs for climbing/crawling to pouches i.e. developed forelimbs might be a necessary criteria but not a sufficient one.

So, between E & D, I picked D since E was too extreme

Experts, Please help me here. Thanks in advance.

i was quickly down to D and E.
On carefully reading D, one would notice that it states about marsupial lions being capable of crawling into their mothers' pouches with their forelimbs. it already takes this fact into consideration that marsupial lion mothers have pouches.
E states that one would not have a matured body part unless that part is matured to be put into use.

the crux of the argument is that one can climb into pouches if it has matured forelimbs.
hence E for me.