The correct answer to this open question is the following.
You forgot to include the options for this question. However, we can say the following.
Whereas the trade to and from Africa is very advantageous to Great Britain and necessary for supplying the Plantations in the Southern Colonies...
Great Britain benefited so much from the Atlantic Slave Trade. In those years, that was the way Britain could supply African slaves to the North American colonies so they could work on the farm fields, under the rule and supervision of the landlords who owned large plantations. The slaves were needed to produce the cash crops that were traded to other American colonies and also were exported to Europe.