Hi Alexandra —
With (D), the hosts a blanket general statement about the universal characteristics of humans and apes based on a single one-month experiment — so, (D) matches several of the characteristics (too general, short term doesn’t account for making such blanket statement) that make the reasoning flawed.
With (B) — without us making assumptions, understanding stock reports is not necessary for investment success — one could be a great investor without understanding them and one could be a terrible investor despite understanding them — and same with being able to make “reasoned” decisions — that has no direct bearing on being better at investing any more than being reasonable about hitting a baseball makes one better at hitting a baseball — also keep in mind that the answers must relate not just specifically with the conclusion, but with the conclusion-premise relationship — and (B) is the one answer here that doesn’t have to do specifically with issues between what the specific details mentioned in the support (one short term experiment) and what was mentioned in the conclusion.
HTH — Mike