About 100 years ago, of people lived on farms in rural areas.
a. 20 percent
b. 80 percent
c. 60 percent
d. 50 percent

I am pretty sure that about 100 years ago, 60 percent  of people lived on farms in rural areas. I consider this option as the most suitable one as in this perion of time in most of rural areas there was quite  nice conditions for setting a farm and growing plants in there. It was good both for life and for bussiness, so a lot of people support the idea of living on farms.
Do hope that helps!