Answer:
Prevalence.
Explanation:
Proliferation means to have a rapid increase in numbers.
Aggression means to have hostile or violent behavior towards others.
Competence means to do something successfully or efficiently.
Prevalence is the state of being widespread or frequent.
Fallibility is the tendency to make mistakes or be wrong.
Based on these definitions, Proliferation would probably go with prevalence, even though competence is also a mediocre synonym.
