Answer:
C. snowball sampling
Explanation:
Snowball sampling also known as referral sampling or chain sampling is a sampling method in research where the participants in the research are recruited to find new participants. This is a non-probability sampling method because participants choose other participants through their own insight. Just as a ball takes up more snow as it rolls by, so also this research method takes up more participants as it progresses.
So, when the field researcher who wanted to learn about a political organization's recruiting pattern begins by interviewing a participant who in turn suggests another participant, he has applied the snowball sampling method.