Tobacco products have been identified has mutagens. however, some tobacco users develop cancer and some do not. the reason for this apparent inconsistency is

A mutation is single change or alternation or multiple changes in the genome of the living organism. A mutagen is an agent which causes mutation. Tobacco products have been identified has mutagens. Some tobacco users develop cancer and some do not this is because of many reasons like : high levels of nicotine and nitrogen is necessary for producing smoke concentration in products like beedi, cigarette which have collectively high mutagenic potential, the age of tobacco leaves used for making tobacco products (old age leaves induce mutagenic potency higher then young leaves), tobacco products with low sugar content will be less mutagenic then with higher sugar contents. Also, the frequency of use of tobacco products also affects the level of mutagenicity. Higher the frequency of use, higher will be chances of occurrence of mutation. Therefore, cause of cancer is chiefly dependent upon the composition of tobacco products and frequency of their use.  

the correct answer is b

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.