The correct options are
B This region experiences a freeze-thaw cycle of alternate freezing and thawing of the ground.
C This biome roughly accounts for 10% of the earth's surface.
D Permafrost is also an important feature of this region.
The Tundra region is charecterised by extremely cold climates that is not conducive for vegetative growth. Thus, the number of species of plants and animals is relatively lesser when compared with other regions. This region experiences a cycle of alternate freezing and thawing. The frozen ground liquifies up in warmer climates in the summer. Permafrost - perenially frozen ground, is also an important feature of this region. Also, the global extent of the tundra biome is considerable. It occupies around 10% of the Earth's surface.