Answer:
a. observer as participant.
Explanation:
There are four major types of observational research of which one is observer as participant.
As researcher carrying out an observational research as an observer of participant , it enables the researcher to carry out observations by collecting data with limited interaction with the participants.
The researcher is recognized by the participants in the study as researcher and is also able to participate in group activities, put as much as possible tries to play a neutral role while carrying out the study.
Therefore, based on the illustration given in the question, the researcher is best referred to as an observer as participant.