What led to the development of the transatlantic slave trade?

The transatlantic slave trade began  in the 15th century, after the Portuguese started exploring the coast of West Africa. At first the number of enslaved Africans was small. In about 1650, with the development of plantations on the newly colonized Caribbean islands and American mainland, the trade grew.

seeing as no choices were provided, i'll do my best to answer it from knowledge.

job specialization promotes work ethic to the person doing the job. he/she may be strong in the arms and able to lift things, specializing him/her in a job where you lift and carry.