The harsh condition in which bristlecone pine trees live may help to explain their exceptional longevity, (because those same conditions are also inhospitable to) the pest that can attack the trees.
a)because those same condition are also inhospitable to
b because those same conditions were inhospitable also for
c) he same conditions being also inhospitable with
d) since those conditions that are also inhospitable to
e)those conditions are also inhospitable to
You only have a comma before the part you can change, and before that comma is a complete thought (AKA an independent clause), so you need to make sure whatever you choose is not a complete thought otherwise you’ll create a run-on. Choice A is the only one that does this without creating any weird verb disagreement.