Passage Summary: A study found that first-born kids are less open-minded than their younger siblings, and since open-minded people are usually adventurous, the younger kids are probably the more daring ones.

Conclusion: Younger siblings are generally more adventurous than their first-born counterparts.

Reasoning: First-borns are less open to new ideas, and there is a correlation between being open to ideas and being adventurous.

Analysis: The psychologist's argument hinges on the link between 'cognitive plasticity' and 'adventurousness.' While the author claims it is 'reasonable to think' they are related, the argument would be much stronger if we had actual evidence of this connection. To strengthen this, look for an answer that confirms that people who are willing to accept new ideas (the study's metric) actually behave in adventurous ways in real life. This bridges the gap between the study's data and the final conclusion.