Final answer:
The long-term trend in American union membership is a steady decrease (option b). Despite shifts in the economy, such as more women working and a larger population, these factors have not caused long-term trends in U.S. unemployment rates.
Step-by-step explanation:
The long-term trend in American union membership has been a steady decrease. The proportion of U.S. workers belonging to unions has declined dramatically since its peak in the early 1950s. Various economic events such as globalization and advancements in technology, along with shifts in the types of jobs which make up the economy, have all contributed to this decline.
It's interesting to note that, although there has been a significant change in the makeup of the workforce and the number of people working, these changes have not resulted in a long-term upward or downward trend in the U.S. unemployment rate. Despite the U.S. population increasing and more women joining the workforce, the economy has managed to provide jobs without causing long-term shifts in unemployment levels.