In the 1840s, the main argument in congress over the transcontinental railroad concerned the geographic direction of the railroad. the money needed to fund the railroad. the lack of available workers to build the railroad. where the railroad should begin in the east.

Hm this is a hard question, as more than one options are partially true, but I think that the best answer is the first one: concerned the geographic direction of the railroad  (if I understand correctly that this is one of the options): Two roads were proposed, Northern and Southern, and this argument corresponded to the general conflict between the North and the South.

However, there was also a dispute concerning where in the East the railroad should start and how it would be founded; but those are more consequences of the conflict described above.