After carefully reading through the following excerpt from "Hidden Figures," answer the question.
Human computers were meticulous and detail-obsessed number crunchers. They would make the necessary calculations for all aspects of flight and design. Sine and cosine, trajectories, curves, fluid dynamics, etc. Everything electronic calculators can do now they had to do by hand. They used tables, graphs, mechanical adding machines, and their minds. One human computer would be responsible for thousands of calculations per day.
What organizational structure is used here?

A. Description
B. Comparison/contrast
C. Problem/solution
D. Sequence