有一道逻辑题不太理解

[url=]Every fall Croton's jays migrate south. The jays always joinflocks of migrating crookbeaks with which they share the same summer and winterterritories. If a jay becomes separated from the crookbeaks it is accompanying,it wanders until it comes across another flock of crookbeaks. Clearly,therefore, Croton's jays lack the navigational ability to find their way southon their own.[/url]Which of thefollowing, if true, most strengthens the argument above?

窗体顶端

·      ACroton's jayslay their eggs in the nests of crookbeaks, which breed upon completing theirsouthern migration.   

·      BThe threespecies most closely related to crookbeaks do not migrate at all.   

·      CIn the spring,Croton's jays migrate north in the company of Tattersall warblers.   

·      DSpecies otherthan Croton's jays occasionally accompany flocks of migratingcrookbeaks.   

·      EIn the spring,crookbeaks migrate north before Croton's jays do.   

答案是C。但是原文作者的观点，J这种鸟缺乏自己南下的导航能力。 问题是要加强作者观点。

那么C选项，说这种J的鸟，在北上的时候也要跟着TW这种鸟。我感觉并没有加强作者观点啊，一个是南下，一个是北上，两回事吧