Answer: b. randomly select people from all residents of the apartment building.
Explanation:
This issue at hand concerns all residents of the building so the apartment manager should randomly select people to participate in the survey from the entire population of all the residents of the apartment building.
Selecting only those who have children would not be representative of the whole population as there will be people with less or more children than 5 and some would not have children. Option C and D are wrong because only current residents should be included.