How were the viet cong able to resupply and strengthen their air defenses

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.

it would be d). more resources must be obtained to attain that combination of goods and services

permafrost layer, it exists beneath a layer of soil, rock or sediment.

answer do so moderately;