I fear I'll never get a perfect score in an LR section...

Always end up going -1/2/3, and I always end up narrowing down do two answer choices, but invariably choose the incorrect one. Ugh!
Can someone walk me through PT 58, LR1 Q11? I narrowed it down to A and B, but of course I chose b. How is b not the correct answer? I reasoned that b was correct because it still raises the possibility of a causal connection. Also, to whomever helps me out, could you do it so that your explanation is structured in Manhattan/LSAT trainer terminology? (i.e, conclusion and then support, and where the gap in reasoning is). Thanks.
Also, I can't believe I got this one wrong, but on question 24, am I correct in my reasoning?
I initially but D because if the population outside the Abiimac Valley outside the Kiffer Forest Preserve is decreasing in population, then it raises the possibility that it is decreasing because these bears are coming into the forest preserve (therefore, the bears aren't increasing from within, the bears are just finding a way in). But I can see how that doesn't completely weaken it as E does. Since E posits that the bear population in the Abbimac Valley has remained the same over the eight years, then this definitively establishes that the bear population may have doubled, but that is because the bears from outside the reserve are getting in. Therefore, the population of the overall valley will not increase if the road is kept closed.