Lost in his own revery, he forgot that vicissitudes can change the course of man's life.

Answer: Option B

Difficulties : the state or condition of being difficult.
Change : make or become different.
Impediments : a hindrance or obstruction in doing something.
Unfortunate : having or marked by bad fortune; unlucky.
Vicissitudes : a change of circumstances or fortune, typically one that is unwelcome or unpleasant.

Synonym of Vicissitudes is Change