(Please Help) A small city conducts a survey to determine how its residents feel about building a public pool facility. Researchers go door-to-door one day from 9:00 a.m. to 5:00 p.m. to ask if the adult resident would like to complete the survey. What kind of sampling technique is being used? Against which group would the survey most likely be biased?

A. Systematic sampling; the sample would be biased against adults who are unemployed.
B. Volunteer sampling; the sample would be biased towards those who complete the survey.
C. Simple random sampling; the sample would be unbiased.
D. Convenience sampling; the sample would be biased against adults who work during the day.