Correct answer:
C) Eastern cities had abundant unskilled labor jobs and well-established Irish communities.
During the Irish immigration at the end of the 19th century there was the construction of the railroad in the East of the country. The Irish were increasingly employed to develop jobs at the bottom of the labor ladder.
Over time, many Irish people climbed occupational and social scales through politically designated positions such as police, firemen and teachers.
For the previous reason, subsequent Irish immigration preferred to arrive in the East of the United States.