Answer:
The population is the registered voters in the city. the sample is the residence of the third floor
Step-by-step explanation:
The population is the group that you want to know information about and the sample is a small group of the population that you select to collect the data.
In this case, the purpose is to know whom they would vote for the upcoming city election, so the population will be the registered voters in the city. Additionally, you only ask to the third floors residence of a building, then the sample will be the residence on the third floor.
So, the answer is:
The population is the registered voters in the city. the sample is the residence of the third floor