What factors explain the difference in biodiversity between the tundra and the tropical rain forest?

a) large land area occupied by rain forest provides more space for a larger variety of organisms to live
b) warmer temperatures and higher average rainfall in the tropical rainforest allow more things to survive
c) unlike tropical rainforest, tundra biomes are cut off from oceans by ice, and so they loose access to rich source of food
d) the tropical rainforest is not supportive of predators as the tundra, which allows many more organisms of varying types to flourish