Answer:
B). Oil
Step-by-step explanation:
The findings of huge accumulations of 'oil' in Oklahoma during the period of 1920s led to a significant boom in its economy. As we know, oil is a very useful resource, and such a huge exploration of oil deposits offered Oklahoma an opportunity to flourish the economic growth by promoting imports, establishment, and growth of oil industries, energy resources, etc. This not only causes increased profits but also invites investment and employment opportunities with amazing returns. Thus, Oklahoma underwent substantial development in its economy. Hence, option B is the correct answer.