Matt and brad own a ice cream store and they believe they have the best ice cream in town. they invite ten of their closest friends to their ice cream shop, give them free ice cream, and then ask for their opinions. brad and matt encouraged their friends to try other ice cream shops, but they told them that they would have to buy the ice cream there. after a week, matt and brad took all the participants out to dinner and 90% of the "tasters" voted matt and brad's shop to be the best in town. which of these would not lead to bias in this experiment? a)matt and brad took the participants to dinner. b)only ten participants were used in the experiment. c)only friends were used in the experiment, and friends will quite often be nice to each other. d)the "tasters" received free ice cream from matt and brad, but they had to pay for it at the other shops.