Which Health Concern Was Supported Empirically as a Reason E-Cigarette

Which health concern was supported empirically as a reason e-cigarette usage is just as dangerous as conventional cigarette smoking?

A) E-cigarettes have lower nicotine and carcinogenic material content.
B) Flavoring used in e-liquids were found to contain toxic chemicals not found in conventional cigarettes,
C) E-cigarette use lowers the probability of other tobacco product use.
D) E-cigarette vapor is less toxic than tobacco smoke because it does not contain nicotine.