Available choices:
i. The number of individuals.
ii. sub-units of species.
iii. the Arctic.
iv. different organisms' numbers.
v. ice.
vi. biological diversity.
vii. penguins.
viii. heat and light.
Given those answer options, answer the question: You are presented with the quiz "What increases in habitats from the poles to the equator?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "biodiversity generally increases from the poles to the equator" and "biodiversity is equated with the number of different organisms present in a habitat ". So, what's the best answer to the question?
A:
iv.