An annually conducted, nationwide survey shows a continuing marked dec

Option B for me.
(A) Changes in the level of drug use by high school seniors are seldom matched by changes in the level of drug use by other people below the age of 20. Weakens the conclusion

(B) In the past, high school seniors were consistently the population group most likely to use illegal drugs and most likely to use them heavily. Correct one as this is the group that uses most of the illegal drugs if the usage in that community decreases the usage of drugs for people under the age of 20 also decreases.

(C) The percentage of high school seniors who use illegal drugs is consistently very similar to the percentage of all people below the age of 20 who use illegal drugs. Wrong. If there are 10 HS students and 1% uses drugs so only 1 guy uses drugs now if there are 100 other people who are under the age of 20 and only 1% uses drugs there are now 10 people in that bracket. So if 1 HS guy now stops using drugs no way it shows the number of people in the age group of 20 is also not using drugs.

(D) The decline revealed by the surveys is the result of drug education programs specifically targeted at those below the age of 20. ( Provides no connection between school seniors and people below the age 20) Irrelevant

(E) The number of those surveyed who admit to having sold illegal drugs has declined even faster than has the number who have used drugs.(same issue, no link between school seniors and people below the age of 20) Irrelevant