Sand is mined from a location in order to make concrete. Growing cities use large amounts of concrete to construct buildings and roads. Which of the following is something an engineer might ask about sand mining and concrete use? Select all that apply.

a
What is the cost of concrete as compared to the alternative material?
b
Why are cities growing so quickly?
c
How does the strength and durability of concrete compare to the strength and durability of the alternative material?
d
What is an alternative material?