Which one of the following choices best represents a potential stressor?
a. an unexpected visit
b. a long-awaited salary raise
c. a surprise gift
d. a decrease in gas prices

I think that B, C, and D, would rather be good news in most typical circumstances, and only in some very atypical ones could they qualify as a stressor.

 On the other hand, A is a potential stressor: you could be unsure whether your house is clean enough for the visit!