Sentence Correction

Hi there....
Here is a quiick question. I am confuse about when to use "they" or "these". Can somebody help me here please:

Factories in southern states like Georgia and Missisipi employed more than 300,000 workers in the late ninteenth century, but they were driven out of business by increasing federal taxes as well as a labor supply that migrated north in the hope of finding better wages.

a) same
b) More than 300,000 worker had been employed by factories in southern states such as Georgia and Missisipi in the late ninetheen century, but they
c)In the late ninetheen century, more than 300,000 workers were employed by factories in southern states such as Georgia and Missisipi, but they
d) More than 300,000 workers had been employed by factories in southern states like Georgia and Missisipi in the late ninetheen century, but these factories
e) Factories in southern states such as Georgia and Missisipi employed more than 300,000 workers in the late century, but these factories

I am between a and e.