The southern colonies practiced indentured servitude and slavery because

Cash crops such as tobacco and sugar required many workers, is the right answer.

Explanation:

The weather of the southern states was warm due to which farming was possible in these states. Accordingly, the landowners began the cultivation of various cash crops such as sugarcane, sugar, rice, tobacco etc. Since these crops were labor intensive, the landowners required a huge supply of labor. Therefore, to fulfill the supply of labor the landowners took interest in the slave trade.

d. japan's attack on pearl harbor