C. Announced an increase in the legal purchase age for cigarettes from 18 to 21.

Furthermore, later in the paper they reinforce this point more specifically, writing: "the cross-sectional nature of our study does not allow us to identify whether most youths are initiating smoking with conventional cigarettes and then moving on to (usually dual use of) e-cigarettes or vice versa...".

Thus, the authors readily acknowledge that it is impossible from this study to determine whether or not e-cigarettes lead to smoking or whether smoking leads to e-cigarette experimentation.

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