题目内容：
根据下面材料，回答题。Smoking Can Increase Depressive Symptoms in Teens
While some teenagers may puff on cigarettes to "self-medicate" against the blues, scientists at the University of Toronto and the University of Montreal have found that smoking may actually ____1____ depressive symptoms in some teens.
"This observational study is one of the few to examine the perceived____2____benefits of smoking among teens," says lead researcher Michael Chaiton, a research associate at the Ontario Tobacco Research Unit of the University of Toronto. "____3____ cigarettes may appear to have self-medicating____4____or to improve mood, in the long term we found that teens who started to smoke reported higher depressive symptoms."
As part of the study, some 662 high school teenagers completed up to 20 questionnaires ____5____ their use of cigarettes to affect mood. Secondary schools were selected to provide a mix of French and English participants, urban and rural schools, and schools____6____in high, moderate and low socio-economic neighbourhoods.
Participants were divided into three____7____: never smokers; smokers who did not use cigarettes to self-medicate, improve mood or physical____8____; smokers who used cigarettes to self-medicate.
Depressive symptoms were measured using a scale that asked how felt too fired to do things: had ____9____ going to sleep or staying____10____; felt unhappy, sad, or depressed; felt hopeless about the future; felt vexed, antsy or tense; and worried too much about things.
"Smokers who used cigarettes as mood ____11____ had higher risks of elevated depressive symptoms than teens who had never smoked," says co-researcher Jennifer O'Loughlin, a professor at the University of Montreal Department of Social and Preventive Medicine. "Our study found that teen smokers who reported emotional benefits from smoking are at higher risk of ____12____.depressive symptoms."
The ____13____ between depression and smoking exists ____14____among teens that use cigarettes to feel better. "It's ____15____to emphasize that depressive symptom scores were higher among teenagers who reported emotional benefits from smoking after they began to smoke," says Dr.Chaiton.
___________ A．examine
B．increase
C．decrease
D．diagnose
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