Answer:
D. lack of genetic diversity in the potato plants
Step-by-step explanation:
The Irish Potato Famine occurred because of successive years of failed crops. The Irish became almost totally dependent on the potatoes as their primary food of source by the 18th century. This led to heavy dependence on this plant for the sheer survival of the population, which makes the population very vulnerable to famine, as the genetic diversity is too small, so a single disease can make enormous damage. That is exactly what happened, as the late blight managed to destroy the potato plants, leaving the country without its primary food source. The end result was large portion of the population dying because of starvation, lot of people were barely surviving, and lot of people migrated out of the country.