Although trains were invented long ago, what kept them from being really efficient?

a-they were too cumbersome.
they ran on wooden wheels.
they could not go uphill.
their tracks were too brittle.

Their tracks were too brittle.

Early train tracks were initially made from iron. Iron is brittle and prone to cracking when trains ran over them repeatedly.

The process of converting iron to steel in an cheap and efficient way changed the quality of railroad rails. Once rails were creating through the Bessemer process and manufactured by Carnegie Steel, the rails help up longer. This also meant trains could be used more effectively and rails could be place all over the country increasing transportation.

judaism, christianity and islam, are all abrahamic religions and therefore have in common the hebrew idea of a single god which is the source of all morality. the idea of the covenant is only related to judaism, while dharma is a concept of indian religions and the four noble truths are basic principles of buddhism.

the china one is last

explanation: