Premises:
A study was commenced ---> Teenagers were selected. ---> The officials of the study saw two things happening: teenagers who took up smoking, within four month were more likely to be depressed than teenagers who did not pick up smoking.

Conclusion: nicotine in cigarettes changes brain chemistry ---> this brain chemical change likely induces depression.

A. Participants who were depressed at the study's start were no more likely to be smokers at the study's end than those who were not depressed. participants who were depressed at the start of the study (G1) and participants who were not depressed at the start of the study (G2). G1 was not MORE likely to start smoking as G2 ---> They have equal inclinations to NOT Smoke. So that means the reverse cause of depression ---> take up smokingis negated If this is true, then maybe our study's officials reasoning is true

B. Participants who began smoking within a month of the study's start were no more likely than those who began midway through to have quit smoking by the study's end. people began smoking within a month (G1). People who left smoking midway (G2) G1 and G2 are equally likely to take up smoking and quit respectively. Does it tell us how nicotine affects brain chemistry to take up or give up smoking? No, we are confused with the relationship. So no clear answer, if true or false.

C. Few, if any, of the participants in the study were friends or relatives of other participants. not important.

D. Some participants entered and emerged from a period of depression within the year of the study. emerging from depression doesnt tell us how nicotine affects brain chemistry

E. The researchers did not track use of alcohol by the teenagers. out of scope.

Ans: A