Answer: The correct answer is- A population with small size is subjected to genetic drift.
Genetic drift can be described as an evolutionary process where a random change occurs in the frequency of a gene variant ( that is called allele) in a population. It can occur in population with all size but its effect is highly pronounced in case of small population. In other words, small population is subjected to genetic drift.
Random genetic drift is primarily caused due to severe reduction in the size of population called "bottlenecks" and founder events, in which a new population is established by small number of individuals.