Select the correct answer. According to the safety valve theory, what would occur once the American frontier was closed?
A.
The concept of what it meant to be American would be changed by Influxes of immigrants.
OB.
The population of the country would quickly overwhelm its natural resources,
Ос.
Social conflict would increase because citizens would not have any place to make a fresh start.
OD.
Economic growth would halt because businesses would not have new markets to conquer.