Sarah felt very anxious after shaking hands with someone who looked like he had a cold, but washing her hands made her feel better.

Obsessive-compulsive disorder.

Explanation:

Obsessive-compulsive disorder: In psychology, the term "obsessive-compulsive disorder" is determined as a mental disorder in which a person feels or experiences unwanted and recurring ideas, thoughts, and sensations which is referred as obsessions that generally makes the person driven to perform a specific task repeatedly and is referred as compulsions.

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

a.indigo and cochineal

b.animal hides

c.silver and gold

e.cacao beans and sugarcane