Which of These Is One of the Three Principal Ways

Which of these is one of the three principal ways in which slavery contributed to the economic development of Great Britain?

A) Slavery encouraged the migration of poor white English people to North America.
B) Slavery provided an enormous stimulus to the growth of European manufacturing.
C) Slavery strengthened the military position of the British in North America.
D) Slavery strengthened the social and cultural bonds between white colonists and the mother country.