Why are some conflicts described as "external"?
they are minor problems in a story.
they pit a character against an outside force.
they relate to events that happened in a character's past.
they refer to political struggles taking place in a character's world.

An external conflict is often contrasted with an internal conflict: a conflict within the protagonist (for example between what he or she should and wants to do).

An external conflict is a conflict between the protagonist and some other force: nature, state or another person.

From the options, the best answer is the following one:
They pit a character against an outside force.