Some analysts suggest that inner-city riots have frequently occurred when poor people realize that their chances of climbing out of poverty are unlikely because of the structure of our social system. Their frustration is based on their perception that they are living in a(n) .

closed stratification system.                          

Explanation:

Social stratification system is defined as a system through which a particular society tends to rank different categories of individuals hierarchically. Therefore, the stratification system is considered as either open or closed.

Closed stratification system: It is referred to as a system that allows a very little change or alteration in the "social position". In other words, it states that an individual gets a little or no chance of moving towards another level in a particular society and therefore a person in the same society or place where he or she has been born.

In the question above, the given statement signifies the "closed stratification system".