GMAT Critical Reasoning (CR) | Re: Although it is sometimes claimed that consuming caffeine at

C for me as it says that people suffering from Insomnia do not respond to their Insomnia through drinking more coffee or tea...it means that people taking coffee or tea in excess were not those who developed Insomnia Before taking coffee in excess. In other words, this option rule out that Insomnia leads to excess intake of Caffeine.
Argument says: A causes B--->we have to make sure that there isn't another thing causing B or its B that causes A.
Option C rule out the 2nd option that B causing
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