Which of the Following Is True About Biomes in General

Which of the following is true about biomes in general?

A) Because evolution occurs over millions of years, the boundaries between biomes can be considered to be static over our lifetimes.
B) Biome boundaries are abrupt, with very distinct differences in appearance from one side of the line to another.
C) Biogeographers disagree on how many biomes there are, and which types of landscapes should be considered part of the same biome.
D) Biomes only exist over land areas.