All the options listed are valid causes of famine in Africa. However, among these options, C. Crops can be sold for more on the world market than domestically is the one that may not directly cause famine but rather reflects an economic decision that can lead to food insecurity. This choice implies that even if food is produced, it might not be available for local consumption if it is prioritized for export, which can exacerbate food shortages but isn't a direct cause of famine in the same way the other options are.
Thus, if you are looking for the option that doesn't fit as a direct cause of famine, it would be C.