The fact that researchers use systematic observation to study human behavior illustrates which of your text’s unifying themes?

depends on what they need

the correct answer on edgen is:

(c.) prevent the spread of communism.

i just took the test.

the secretary of state, appointed by the president with the advice and consent of the senate, is the president's chief foreign affairs adviser. the secretary carries out the president's foreign policies through the state department and the foreign service of the united states.