"Therefore" is used to draw a conclusion based on previous statements. In this case, it logically follows from the idea that animals may or may not predict certain events, leading to the conclusion that we shouldn't completely dismiss their abilities.
Hence, option (d) is the answer.
"However" introduces a contrast, but the sentence doesn't set up a direct opposition. It would imply a stronger contradiction than is present here.
"Nevertheless" also introduces a contrast, suggesting a stronger opposition than is warranted in this context. It's not the best fit for a concluding statement.
"Moreover" adds supporting information, but the passage is drawing a conclusion rather than adding more details, so it's not appropriate here.
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