Fragile ecosystems cover:

A.The arid and semi-arid zones of the world, arid savannas of the tropics, the slopes of the mountains of the tropics
B.And subtropics and forest areas of the developing world under shifting cultivation have been described as ‘Fragile Ecosystems’
C.Because their equilibrium appears to be easily upset and because they become ecologically degraded if certain forms of land use
D.All of the above