Show all work

13. A survey is conducted which takes a random sample of 500 Utah County households. The survey asks what the household income is for each sampled house. Of the 223 responses, the average income was $76,132. More than half of the sampled households did not respond. Any errors due to the nonresponses (3 pts) a. Can be accounted for with a 99% confidence interval. b. Are included in the margin of error. c. Are in addition to the random variation accounted for by the announced margin of error. d. Have no effect on the accuracy of the confidence interval