Every weekend in summer, large numbers of people leave the hot desert climate of phoenix to head for vacations in the cooler climates of northern arizona. this is an example of

Most likely cyclic movement. 

Answergovernment control over all imports and exports;

Historians are researchers of the past or people who understand the history of people. with this field, they must possess qualities such as being unbiased, patient, efficient reader, has a knack for logic and critical thinking and reasoning, disciplined, open-minded, resourceful, with good analytical ability, good reasoning skills and problem solving!