Why did the dust bowl occur?

Crops began to fail with the onset of drought in 1931, exposing the bare, over-plowed farmland. Without deep-rooted prairie grasses to hold the soil in place, it began to blow away. Eroding soil led to massive dust storms and economic devastation—especially in the Southern Plains.Aug 5, 2020

Explanation:

This happened because of drought.

In this economic depression there was drought, there was no grass. There wasn't anything to keep the soil in its place. And because of this, huge dust storms happened. And thats why its called the dust bowl.

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.

the answer is a) high entry costs