Final answer:
To prepare for his book 'The Grapes of Wrath', John Steinbeck took a job as a migrant worker to gain firsthand experience and a deeper understanding of the struggles and hardships of the migrant farmers.
Step-by-step explanation:
In preparation for his book The Grapes of Wrath, John Steinbeck took a job as a migrant worker. This firsthand experience allowed him to immerse himself in the lives of the migrant farmers he would write about. By working alongside them, Steinbeck gained a deeper understanding of their struggles and hardships, which ultimately contributed to the authenticity and realism of his novel.