The correct answer is intruder.
B. participant in a dialogue
The correct answer is (C) Intruder; meddler; one who intrudes on the property of another; someone who meddles in the affairs of another; to intrude into a field of endeavor or region without proper authorization.
Interloper comes from Inter + loper (leap).
Examples of use:
- We were prepared to use force to expel any interlopers from our property.
- To his chagrin, interlopers effectively destroyed the meeting's utility.