Climate, more than any other single factor, determines the distribution of life on earth. Climatic boundaries establish the limits within which organisms can survive. Plants, even more than animals, must be well adapted to climate in order to survive. They cannot move about or take shelter but must be equipped to endure whatever weather conditions. In the cold north pole, for example, low growing mosses(苔,藓) all hug the ground for shelter from icy winds.
Animals, despite their ability to move about and find shelter, are just as much influenced by climate as plants are. Creatures such as the camel and the penguin are so highly specialized that they have an extremely limited distribution. Others, such as bears, are flexible enough to adapt to a broad range of climates. Ocean-dwelling organisms are just as sensitive to climate changes in this temperature and salinity as land animals.
Human beings are among the least specialized of all animals and live almost anywhere. Their clothes and their homes act as a sort of "miniature climate" that can be taken with them everywhere.According to the passage, which of the following factors most influences where life is found on earth（）

A．Climatic conditions.
B．The length of days and nights.
C．Ocean tides.
D．Geographic boundaries.