Which one of the following would some say invalidates the unbiasedness hypothesis?

Question

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The Siegel paradox suggests that high beta stocks actually earn lower returns than predicted by the Capital Asset Pricing Model (CAPM), which is based on the assumption of unbiasedness. This contradicts the unbiasedness hypothesis and implies that there are factors other than risk that affect stock returns. The Fisher Effect, efficient market hypothesis, and the law of one price are all consistent with unbiasedness.

Which One of the Following Would Some Say Invalidates the Unbiasedness