The answer is either B or C
A mainly because none of the others are even close to warnings sins and i have my notes and i had this on my health test
The fear appeal is a common thing used in the media and basically boils down to trying to get someone do what you want them to do by providing them with an example that strikes fear if they wouldn't do that. A recent example would be Trump and his rhethoric about Mexicans and Muslims.
Communication barriers can be physical disabilities such as hearing problems or speach problems but it can also be the lack of interest, attention differences in viewpoint etc.
