During the Great Depression, thousands of people changed social class unexpectedly, usually in a downward spiral. This event was the impetus for a type of social mobility called mobility.

Structural mobility

Explanation:

In simple words, Whenever societal developments allow a large number of individuals to migrate upward or bottom the economic class hierarchy, this is known as structural movement. Individual improvements are not responsible for structural mobility; rather, it is due to developments in community as a whole.

Thus, from the above we can conclude that the correct answer is structural mobility.

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