What event caused increased the numbers of settlers in the west, the range of commerce and contributed to the growth of cities like chicago and denver?

Chicago  became a transportation and commercial center in 1850's. The extraordinary growth of the city in the 1850's was attributed to the rapid increase of railroads namely the Galena & Chicago Union Railroad and their effects which made transportation and trading of goods easier than the previous method of trading by steamboats. Moreover the direction of trade shifted from north-south to east-west.

The settlements in Denver increased in 1858 due to the Pike's Peak Gold Rush.This was the first historical settlement in the city of Denver.

seeing as no choices were provided, i'll do my best to answer it from knowledge.

job specialization promotes work ethic to the person doing the job. he/she may be strong in the arms and able to lift things, specializing him/her in a job where you lift and carry.