Blue Ribbon taxis offers shuttle service to the nearest airport. You look up the online reviews for Blue Ribbon taxis and find that there are 17 reviews, six of which report that the taxi never showed up. Is this a biased sampling method for obtaining customer opinion on the taxi service?

a. This is not a biased sampling method for obtaining customer opinions because those who take the time to write an online review are choosing to write the review without any incentive.
b. This is a biased sampling method for obtaining customer opinions because those who take the time to write an online review are likely to do so because they are satisfied with the service they received.
c. This is a biased sampling method for obtaining customer opinions because those who take the time to write an online review are likely to do so because they are upset with the service they received.
d. There is not enough information to tell if this is a biased sampling method.

Based on reviews we cannot conclude whether the sampling is biased or not, if only we can know the total number of times the taxi was ordered then we can conclude.

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