sometimes you should know what is required condition and what is sufficient condition.. for example, when the passage talk about "only if, assumption, unless..." but in this passage, "prior" means a comparision..therefore,you don't need to think about what is required condition and what is sufficient condition... in this passage, you should finish the passage by providing a reason why sales person should not emphasize on the the user-friendly characteristic of computers.. b is wrong because without addition information we can't clearly explain the reason why sales persons should not emphasize on the user-friendly characteristic..for example, if people care more about user-friendly than money, we can't use B as an reason to explain the argument... e tells us that comsumers concen more about whether the cost of user-friendly computes worth the expense, and therefore give an explanation to the conclusion the arguer makes.. | 
