What was the connection between the development of steel and the development of railroads?

The railroads were the biggest customers for the steel industry because thousands of miles of steel track were laid. In turn, the railroads had a great impact on the steel industry. To supply their biggest customers, steel producers developed cheap, efficient methods for the mass production of steel rails.

Explanation:

the answers are 1 and 4

d is the answer. leo should include the source.