Which of the following must occur in order for an ecosystem to continue to exist? А
The populations of producers and decomposers must be stable.
B
The populations of animals must continue to decrease.
С
There should be more populations of consumers than producers.
D
There should be fewer populations of producers than consumers.
Ok

A, the populations of producers and decomposers should be stable

Explanation:

The other three do not fit, only reasonable one is A

the truman doctrine was an american foreign policy whose stated purpose was to counter soviet geopolitical expansion during the cold war. it was announced to congress by president harry s. truman on march 12, 1947, and further developed on july 12, 1948, when he pledged to contain threats to greece and turkey.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.