Why Did European Slave Traders in Africa Adopt the "Shore

Why did European slave traders in Africa adopt the "shore method" of trading in the eighteenth century?

A) It secured for Europeans supplies of slaves by establishing fortified trading posts on the coast, thus preventing wasted days at sea looking for slaves to purchase.
B) It gave Europeans more control over the slave trade by sending ashore slave-hunting teams to seize slaves and force them aboard.
C) It relieved Europeans of the moral difficulty of separating families by having all slaves separated into unrelated groups of fifteen before the ships' captains purchased them.
D) It permitted Europeans to move easily along the coast, obtaining slaves at various slave markets and then departing quickly for the Americas.