Final answer:
The Bantu prepared the land for planting crops by selecting favorable sites, such as fertile river valleys, and adapting their cultivation techniques to different environments.
Step-by-step explanation:
The Bantu prepared the land before planting crops by selecting the best sites for farming in fertile river valleys and regions with favorable rainfall. They did not need to clear thick forests or adopt new techniques to suit difficult environments, so their expansion across the subcontinent proceeded rapidly. As their population grew, they began to move into the rainforest, gradually occupying all parts of it, and adapting their cultivation techniques to a variety of conditions.