Your question asks how critical life events affect leadership.
The reason why answer choice "B. They act as a catalyst for change" would be the correct answer because the events can cause a change in a person.
Catalyst means something that causes a change.
Critical life events could cause a change in an individuals actions and/or thoughts, including an affect in their leadership.
For example, someone who leads a football team recently lost their mother to a car accident, the football leader would possibly feel hurt and wouldn't want to participate in the sport.
This shows how critical life events acts as a catalyst on people's leadership.