Which of the following is true of Dust Bowl migrants? They were lone transients who rode the rails in search of adventure. They were...

Of the options given in your question, the only possible
answer is #4.  Answer #1 has an element of truth in that some of the Dust Bowl migrants
did become hoboes, but it was generally not a search for adventure that drove them. 
Instead, it was poverty.

During the Dust Bowl, hundreds of
thousands of people had to leave the plains states in search of new homes where they
could hope to make a living.  These people tended to be generically known as "Okies." 
As you can see in pictures such as those by Dorothea Lange, the Okies tended to migrate
in family groups as they looked for a way to make a living.