What landform has the most impact on population distribution in south asia?

Mountains

Explanation:

Mountains such as the Himalayas because they provide water to the rivers of the South East Asia, being able to the rice irrigation and protein to tens of millions of South East Asians in Thailand, Laos, Vietnam, etc.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.

answer; utilitarian;