Stress can emerge
a. only from events that are important.
b. from both positive and negative events.
c. only from negative events.
d. only from positive events

Stress can emerge from important events. but also from less important ones, even from being 2 minutes late for a social event! So A) is false.

There is a positive, motivating kind of stress, and a negative, debilitating one. So the correct answer is: it can emerge b. from both positive and negative events.

Stress can emerge : B. From both positive and negative events.

Example , 
Positive : Stress that all the brides have before the wedding ceremonies
Negative : Stress that are caused after someone was fired from his/her job

hope this helps