NOT A marketing firm conducted a survey of brand recognition. They constructed a confidence interval for the true mean of price of a product of a certain brand. Which of the following sources of error are included in the margin of error for the true mean price of the mentioned product? Select one: O a. Some respondents used to buy the product at alternative resellers and consistently stated a lower price. O b. Undercoverage bias - the firm did not plan the survey so that a fairly random sample participated. O c. Some respondents did not recognize the brand and therefore were just making up a price. O d. Chance variation of choosing a random sample of participants