Researchers divided a group of people on the basis of their smoking status (smokers and non-smokers) and followed them for 20 years to see if they developed lung cancer. This is an example of what type of epidemiological research design

Cohort

Explanation:

Cohort studies refer to a form of medical study which is used to examine the reasons for the disease and to find its relation to the risk factors to medical outcomes. Usually, cohort studies track large groups of people, tracking their susceptibility to such risk variables in order to obtain answers to the potential causes of disease.  

As per the question, researchers observe a group of people based on their smoking habits and tracked them for twenty years to observe its relation to lung cancer reflects the procedure of cohort studies.

according to hess's theory, when the magma cooled, it would expand and push the tectonic plates apart. it would push the north and south america plates to the west and eurasia and africa ones to the east. the atlantic ocean would get wider but the coastlines of the masses would stay the same.

harry hammond hess was a geologist and a united states navy officer in the second world war. he is considered to be one of the founding fathers of the theory of plate tectonics. he is known for his theories on sea floor spreading, stating that the movement of the continents was the result of see floor spreading. the continents are attached to the plates and do not move separately. the plates themselves shift and change shape, carrying the continents along.

answer; the intervening variable;