The Maasai Have Faced Increasing Difficulties Practicing Transhumant Pastoralism Primarily

The Maasai have faced increasing difficulties practicing transhumant pastoralism primarily because:

A) Global warming has made grasslands scarce.
B) Government taxation policies have radically reduced the sizes of their herds.
C) Men now have the choice of herding or working in the tourist industry and most frequently choose the later.
D) Cattle diseases have made herding impossible in much of the land the Maasai inhabit.
E) The required grazing land has been taken from them.