Final answer:
Calvin Coolidge suggested that when many people are unable to find work, it results in economic depression. This situation was evident during the Great Depression, where high unemployment led to widespread economic hardship and people lined up for relief checks.
Step-by-step explanation:
Calvin Coolidge is reported to have said, "When a great many people are unable to find work," this results. The correct answer among the options provided would be (d) Economic depression. High unemployment rates can lead to economic decline as consumer spending decreases due to fewer individuals earning wages, which can ultimately slow down economic growth and lead to an economic depression. This was the case during the Great Depression, a time when many people were struggling to make ends meet and queued for relief checks, indicating a faltering economy.