Final answer:
The condition that best fits the chart outlining post-World War I advancements is 'C. Assembly lines sped up factory work'.
Step-by-step explanation:
The period following World War I was marked by significant economic and social changes. The conditions listed in the student's question point to various aspects that characterized the immediate postwar era, such as the increase in mass production, the granting of women's suffrage, and the implementation of child labor laws. To identify which additional condition best belongs on the chart, one should consider the transformations taking place in the industrial and consumer landscape of the time.
Given the options, the most fitting condition to add to the chart is C. Assembly lines sped up factory work. This is because, during the post-World War I period, the adoption of assembly lines, particularly popularized by Henry Ford's automobile production, significantly increased the efficiency of factory work, leading to higher output and greater availability of consumer goods. This change was a crucial element of the era's industrial advancement and played a major role in shaping the economic growth that defined the 1920s.
While other options such as business taxes increasing and wages and buying power decreasing might also reflect post-war realities, these are not directly tied to the themes of the chart which focus on advancements and positive changes in production and rights rather than economic hardships.