Passage Summary: Britain uses a quarantine to keep rabies out, but the author argues this won't work forever because you can't exactly put a wild bat in a cage at the border, and they fly in from Europe all the time.

Conclusion: The current quarantine policy in Britain will eventually fail to prevent rabies outbreaks.

Reasoning: While domesticated animals are quarantined, wild bats—which are highly susceptible to rabies—fly into the country from Europe and cannot be subjected to the same controls.

Analysis: The argument employs a strategy of identifying a specific exception that renders a general policy insufficient. It acknowledges the existence of a rule (quarantine for imported animals) but points to a vector (wild bats) that the rule cannot possibly cover. By highlighting this uncontrollable variable, the author concludes that the policy's ultimate goal is unattainable. To identify this strategy, look for how the author uses the 'wild bat' premise to undermine the long-term efficacy of the quarantine.