The correct answer is c) cyclical unemployment.
Cyclical unemployment occurs due to downturns in the economic cycle. During the Great Depression, the economy faced a severe decline, leading to massive job losses across various sectors as businesses closed or reduced their workforce. This kind of unemployment is directly linked to the economic environment—when the economy falters, companies often let go of employees, resulting in higher unemployment rates.
In contrast, frictional unemployment is a normal part of the labor market, occurring when people are between jobs or entering the workforce for the first time. Structural unemployment arises from shifts in the economy that make certain skills obsolete, while core unemployment is less commonly referenced and can relate to factors such as consistent voluntary unemployment or chronic joblessness. Thus, during the Great Depression, it was the cyclical nature of the economy that predominantly drove unemployment rates to historic highs.