Which of the following is not a common farming system in West Africa?

The answer is terracing. Terracing is not a common farming system in West Africa. Crop rotation, rotational bush fallowing, and subsistence farming are common farming systems in West Africa. Crop rotation involves planting different crops in the same field in different seasons to maintain soil fertility and control pests and diseases. Rotational bush fallowing is a farming system where a plot of land is cleared of vegetation and farmed for a few years, and then allowed to lie fallow for a longer period to allow the vegetation to regenerate. Subsistence farming is a type of farming where farmers produce only enough food to feed themselves and their families. It is a common farming system in West Africa, where small-scale farmers grow crops and rear animals for their own consumption. Terracing, on the other hand, is a farming practice where steps are constructed on sloping land to create a flat surface for farming. It is more commonly used in mountainous regions such as Asia and South America, where there is a need to farm on steep slopes.