The reasons why groups of people leave a particular place are known as:
o
a. pull factors.
o
b. push factors.
o
c. negative elements.
o
d. dead-end situations.

B push factors

Explanation:

it could be A or B. but say if the conditions at the place they are currently at are worse that where they are going it would be push factors so I think push is the best option.

the causes of the dust bowls were severe droughts,   lands became dry and hard, temperature was higher than usual, hot and dry conditions killed crops, high winds. because of those factors, the winds kicked up dry soil and created clouds of dust.