Which of the following is an example of agglomeration?
a. a steel mill is located in the country to take advantage of low labor costs
b. a clothing factory is located in the same city as a steel mill and a furniture factory
c. a coal mine is the only business employing workers in 20 miles in any direction
d. a paper mill six to move away from the competing businesses
e. a meat packing plant discourages other companies from moving into the area