What Were the Underlying Causes of World War I and which was the most influential? cited

After world war 1 immigration was based on

How did american entry into world war i affect the allied powers?

Which of the following is an example of the pull factor known as economic migration? a. better educational opportunities pulling people towards a new country b. mexican laborers entering the us to work in agricultural jobs c. joining family members that are already in a new country d. crop failures driving people away from their country i am unsure on this question, i was thinking b? but i could be wrong.