Which circumstance was most directly responsible for the rapid growth of the railroad industry? inventors developed air brakes and more efficient train-car connectors builders agreed on a universal width for train tracks railroad owners sold stock to investors to finance the construction of railroads pullman began manufacturing cars for overnight travel

Option C- Railroad owners sold stock to investors to finance the construction of railroads

This was the most important reason that was directly responsible for the rapid growth of the railroad industry  because constructing railways was a very expensive capital investment business. Hence railroad owners sold stock to investors to finance the construction of railroads.

i believe the correct answer is option b. most eastern european nations joined nato.

though i could be wrong, option d. the eastern european nations were granted complete independence, would be another choice.

hope this ! : )

ghana achieved independence peacefully, while algeria gained independence through an armed struggle.