Scientists believe that many daily rhythms are controlled by an internal
fill in the blank, will decide who is brainliest.

A clock would be the answer.
Circadian Rhythms 

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