@Warren_Chen AC (B) weakens the argument by giving an alternate explanation for what causes depression (or that disposition). Excessive sleep is caused by clinical depression which leads to less left lobe activity. A reversal of a causal relationship is a classic way to weaken a causal argument (like correlation = causation flaw), and introducing an alternate explanation would weaken the argument above.
@Warren_Chen AC (B) weakens the argument by giving an alternate explanation for what causes depression (or that disposition). Excessive sleep is caused by clinical depression which leads to less left lobe activity. A reversal of a causal relationship is a classic way to weaken a causal argument (like correlation = causation flaw), and introducing an alternate explanation would weaken the argument above.