Answer:
https://www.gstatic.com/education/formulas2/355397047/en/elastic_collisions.svg
Explanation:
I think the first big picture is group communication, the second one with the person talking in front of everyone is public communication, and the last one is dyadic communication
C. 340
Frequency is the number of wavelengths per second and since the length is 0.5 you multiply 0.5*686 and get 343.
the question not allowing for one position thus the answer is c