What is John Steinbeck's book The Grapes of Wrath about?

A. The devastation of men working on Wall Street

B. The cause of drought in middle America

C. The solution to the Dust Bowl

D. The struggles facing migrant workers

I'd say that the correct answer is D, merely because all the other options don't seem correct to me. I wouldn't say A is correct because the book doesn't deal with Wall Street, but workers. B isn't correct as well, as the book doesn't focus on the cause of the drought, but its effects. C is also incorrect as people leave Dust Bowl, so in my opinion, the correct answer is the only remaining one - D. The book deals with the struggles of the workers, and their lives, and what they had to do to make for a living.