提问：og_10_115青少年吸烟的逻辑题

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Many people argue that tobacco advertising plays a crucial role in causing teen-agers to start or continue smoking. In Norway, however, where there has been a ban on tobacco advertising since 1975, smoking is at least as prevalent among teen-agers as it is in countries that do not ban such advertising.

Which of the following statements draws the most reliable conclusion from the information above?

(a) Tobacco advertising cannot be the only factor that affects the prevalence of smoking among teen-agers.

(b) Advertising does not play a role in causing teen-agers to start or continue smoking.

(c) Banning tobacco advertising does not reduce the consumption of tobacco.

(d) More teen-agers smoke if they are not exposed to tobacco advertising than if they are.(A)

(e) Most teen-agers who smoked in 1975 did not stop when the ban on tobacco advertising was implemented.

想问A为何对？

假设挪威原先青少年的吸烟率是90%，别的国家是70%。现在挪威禁止广告了，吸烟率下降到了70%。
这不是符合smoking is at least as prevalent among teen-agers as it is in countries that do not ban such advertising.吗？
然而在这种情况下，说明广告还是有用的，而且可能是the only factor that affects the prevalence of smoking among teen-agers.A就不对了啊~
我的理解哪里错了呢？