Passage Summary: People's blood pressure goes up when they talk, but it goes up less for extroverts than for introverts. The author thinks this means the stress of talking causes the rise, not just the physical effort of moving your mouth.

Conclusion: The increase in blood pressure during speech is caused by psychological stress rather than the physical act of speaking.

Reasoning: Extroverts, who find speaking less stressful, show smaller blood pressure increases than introverts, who find it more stressful.

Analysis: To strengthen this argument, we need to bolster the link between stress and blood pressure while downplaying the physical exertion factor. The psychologist is assuming that the only relevant difference between introverts and extroverts here is their stress level. Look for an answer that rules out physical differences, such as one suggesting that extroverts and introverts exert the same amount of physical effort when they speak. If their physical exertion were identical but their blood pressure responses differed, it would strongly support the stress-based explanation.