Which of the following must be true for natural selection to occur? O A. The ecosystem cannot contain predators.
B. A population cannot have competition for resources,
C. A population must be stable.
D. The ecosystem must have limited resources,

D. The ecosystem must have limited resources

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