The 2007 crash of the us housing market was an example of a(n)

The 2007 crash of the US housing market was an example of an economic downturn.

An economic downturn constitutes one of the stages of the economic cycle and  occurs when the value of stocks, property, and commodities fall, productivity either increases more slowly or decreases, and the gross domestic product, commonly known as GDP shrinks, stands still or expands more slowly.

d) all choices are correct

in the 1800s, locomotives powered by steam made transportation faster and cheaper. the resulting rapid growth of railroads led to the connection of the atlantic and pacific railroad in oklahoma city in 1897.

in the last years of the century, the improvement of steam-based engines the expansion and growth of railroads. this growth increased when the companies started to build and expand, such as the atlantic and pacific railroad, which connected new mexico with california, and missouri with oklahoma. many of these new networks were built in oklahoma, and these changes transportation henceforward.