Domesticated herd animals were first integrated into agriculture when they were used A. To assist hunters
B. For their meat and milk
D. To transport harvested crops
E. For their fur and skins
F. To prepare land for planting

B is the answer.

A doesn’t make sense, animals don’t really help hunters.

D doesn’t make sense either, transportation was good but herds of animals usually weren’t only used for that.

E could make sense but usually they already had an abundance of fur and skins from animals they had killed in the past.

F animals rarely help when preparing land for planting and I doubt they knew how to use them for such things, though it’s possible, it’s very unlikely, especially since they just got them.

Answer the use of flood plains and irrigation;