Question

1. why were dust bowl migrants often referred to as okies?

all of the migrants came from oklahoma.
\okie\ was an insulting term that californians made up.
\okie\ was a commonly used slang term for \migrant.\
most of the first migrants to arrive in california were from oklahoma.

Explanation:

Dust Bowl migrants included people from multiple Great Plains states, but the large initial wave arriving in California originated from Oklahoma. The term "Okie" became a catch-all for these migrants because this first major group was from Oklahoma. It was not initially an insult, nor was it a general slang for all migrants, and not all migrants were from Oklahoma.

Answer:

Most of the first migrants to arrive in California were from Oklahoma.