Answer :
The reason the number of people in Agriculture decreased was that C. economic opportunities to work in factories during and after World War II.
Factory jobs during and after the war
- As the U.S. went off to fight in WWII, they mobilized the entire nation which led to factories increasing their output heavily.
- This continued after the war as the government kept investing in the economy to keep the momentum going.
As a result of this, there were many factory jobs available for people such that a lot of people left agriculture for the more lucrative factory jobs.
In conclusion, option C is correct.
Find out more about the economic trend after WWII at https://brainly.com/question/1073353.