Answer and explanation:
The political scientist is investigating "proportion of adult residents
..." and so the subjects of his study can only be found among adults. The units are therefore all adults, including registered adults. The frames can include census data showing adults in a particular area, telephone directories, registered voters in the area etc. If the researcher chooses to use personal interview in collecting data for his research, he would easily get response and also be able to explain questions out more, also there is the benefit of less corrupted data. Using telephone interview would save the researcher and respondents costs as there is no need to travel and the researcher could still explain out questions properly. If the researcher chooses to collect data through mailing respondents, there is alot more flexibility as respondents can reply at their convenience and when they are ready, also subjects may wish to not disclose identity with this data collection method