An example of externalization of behavior as a result of stress is

A. withdrawal.

B. isolation.

C. headaches or stomachaches.

D. outbursts of anger.

The answer is D.) outbursts if anger

Well, which one is "external?" Headaches and stomachaches are known to exist internally, isolation is setting yourself apart which may or may not be noticed, withdrawal is declining yourself from something, while an outburst of anger is very clearly seen and heard by all. All in all, I would say D.