The argument isn't too difficult to take apart: the more well-protected a species the more likely it will live long (think of a tortoise's giant shell); the less well-protected the more likely it will try to procreate as quickly as possible (I'm thinking rabbits here

). By extension, the sooner a species tries to procreate the shorter its lifespan.
As for the best answer, it gets a little trickier...
(A) Tortoises that procreate quickly and at an early age tend to live longer than tortoises that devote their resources to protecting themselves.The real issue is between species. That is, we want to compare well-protected to not-so-well-protected species in terms of longevity. Anyhow, this answer choice apparently goes against the conclusion.
(B) Animals that procreate early, such as fruit flies, have shorter lifespans. ANSWERHere we have an animal that procreates early (the fruit fly, all 50mg of it, just isn't too well protected) try to multiply as soon as possible. Again, the argument is stating that the less well-protected/sooner procreating species tends to have a shorter lifespan. This answer choice is by no means a homerun answer that makes you think, 'hey this is obviously it!' After all, we do not have much information on well-protected/wait-to-procreate species. Nonetheless, the answer lends some credence to the view, so I'll keep it.
(C) The oldest tortoises on record live about twice as long as the oldest humans in history.We need to know a little bit more about when exactly the tortoise starts procreating. Sure, the turtle lives to well over 100 years, but when does it start procreating compared to a human?
(D) Tortoises lay between one and thirty eggs at a time, while other animals may lay hundreds.Sure, but perhaps there are many animals that lay fewer than 30 eggs (and presumably they do not live as long as the longest-living species). Anyhow, we are concerned with the 'when' not the 'how' of procreation.
(E) Tortoises who face less pressure from predators tend to have longer lifespans.Like (A), this answer choice focuses on tortoises. The correct answer has to discuss less well-protected species and their longevity/age of procreation. This answer choice may be tempting because it states something that is logically sound: tortoises that are not prey tend to live longer.
And like that, the only correct answer left standing is (B).
Hope that helps