Some agricultural sub-saharan nations of africa have overfarmed and overgrazed their land to the extent that significant portions of it have turned into desert. this suggests that

a.

congress passed laws allowing for free passage between states.

the fact that could also be added to column b is that during world war ii, specifically between the years 1941 and 1945, japan expanded its territory towards the indonesian territory in what was known later as part of the "pacific war". in that time, japan could conquer the philipines, singapore,   borneo, central java, malang, cebu, sumatra and various other islands of the area, therefore expanding its territory for a brief period of time.