求助一道PREP上面的原题，感谢大家了

mikrodj wrote:
Premise 1: Every fall Croton's jays migrate south.
Premise 2: The jays always join flocks of migrating crookbeaks with which they share the same summer and winter territories.
Premise 3: If a jay from the crookbeaks it is accompanying, it wanders until it comes across another flock of crookbeaks.
This implies that a jay needs a flock to migrate south.
Conclusion: Croton's jays lack the navigational ability to find their way south on their own.
Consider the following problem (perhaps not the best analogy)
David goes to the gym every Wednesday. Every time David goes to the gym, Richard goes with him. If Richard stops to buy something, David waits for him. Clearly, David lacks the navigational ability to find the way to his gym.
what would strengthen this argument?
Every time that David needs to go to the University, he calls Richard to find the way. If the author said that David can go on his own to the university this would hamper the conclusion that David lacks navigational ability.
Regarding the problem
(A) Croton's jays lay their eggs in the nests of crookbeaks which breed upon completing their southern migration.
does this account for the lack of navigability of the croton's jay?
Let me know if this helps. I know my explanation might be not really clear