Answer:
B. search for Depression-era primary sources from cities to see if they mention urban poverty would be the most appropriate way to determine whether the historian's interpretation is valid. By examining primary sources from the time period, such as newspaper articles or personal accounts, one can gain a more comprehensive understanding of the effects of the Great Depression on different groups of people, including those living in cities. This would provide evidence to support or refute the historian's claim that people in cities generally had no idea about the Depression. Option A is not relevant to evaluating the historian's interpretation, while options C and D may not provide direct insight into the validity of the historian's claim.