City authorities are planning an economic revitalization of the downtown area. They want to attract more college graduates to the city who will both reside and work in the downtown area. Which of the following qualitative data collection techniques would be most useful to the city authorities as they begin planning the revitalization?
a. Focus groups with recent college graduates living in downtown
b. In-depth interviews with employers in the downtown area
c. Observational studies of foot traffic and usage of downtown amenities
d. Surveys of college students and recent graduates about their preferences for living and working locations
