A marketing firm for Cobra Auto Security Systems mailed out a survey to 35% of the households in New York City, Washington DC, and Chicago to determine the market for auto security systems. According to the respondents of the survey, 55% of the population uses public transportation and does not own an automobile. So, the marketing firm concluded that 55% of all Americans use public transportation and do not own an automobile. Which of the following statements is correct?
A. This method of sampling is neither biased nor unbiased.
B. This method of sampling can be considered both biased and unbiased.
C. This method of sampling is biased.
D. This method of sampling is unbiased.