What Is the Primary Reason That Caribbean Colonies Began to Turn

What is the primary reason that Caribbean colonies began to turn to indentured labor as a workforce in the mid-nineteenth century?

A) These individuals tended to work harder than slaves.
B) By this period most of the African slaves in the Caribbean colonies had fled to Maroon settlements.
C) There was a need for the highly specialized skills they brought.
D) By this period most of the colonial governments began to free their slaves.
E) By this time nearly the entire African continent had been depopulated.