b. american pioneers in the 1700s
a is not correct because horse-drawn wagons are not used in the 21st century. c is not correct for the same reason - this clearly does not take place in modern times. d is incorrect because prehistoric humans were still evolving and developing from primates and figuring out how to be people. pioneers are people who are the first to do something, usually settling in a place. 1700s were a time fore horse drawn carriages, so b is the only answer that could fit this description