Immigration Has Increased in the Latter Half of the Twentieth

Immigration has increased in the latter half of the twentieth century because:

A) the growing discrepancy in incomes between countries has provided people with enormous incentives to seek "a better life" in another country.
B) improved communications have made people more aware of what life is like in other countries.
C) economic growth has lowered transport costs.
D) All of the above.
E) None of the above.