According to the united nations’ stages of economic development for classifying countries with respect to levels of industrialization, a country that is industrially underdeveloped, agrarian, has subsistence society with rural populations and extremely low per capita income levels falls under the category of
a. first world countries
b. least-developed countries
c. less-developed countries
d. newly industrialized countries
e. frontier markets

The correct answer is letter "B": least-developed countries.

Explanation:

Least-developed countries or LDCs are low-income countries highly vulnerable to economic and environmental shocks and have a low level of human assets. The United Nations Committee for Development Policy (CDP) reviews the list of countries every 3 years and makes recommendations on inclusions and graduations of the countries if eligible. In order to classify those countries, they use 3 criteria:  

* Human assets: imply secondary school enrollment, under-nourishment, maternal mortality, adult literacy and under-five mortality.

* Economic vulnerability: include population, remoteness, export concentration, victims of natural disasters, the share of agriculture and fishing in Gross Domestic Product, share of population in coastal zones, instability of exports and agriculture .

* Income per capita:  according to the 2015 per capita threshold for the graduation of the LCD list is USD 1242.

In order for a country to graduate from the LCD list, 2 out of the 3 criteria must be improved after the review of the CDP in a period of 3 years, twice consecutively.

think its caste system

explanation:

the answer to your question is,

d. when a child was born.

-mabel < 3