In most classification schemes, which principal indicator is used to delineate five zones and their subtypes?
Cloudiness
Temperature
Daylength
Precipitation
Vegetation types

Vegetation types

Explanation:

In the case of biomes, which are perhaps the most commonly used classification scheme in physical geography, vegetation is the principal indicator to delinate the different zones and their subtypes.

Even if both vegetation and fauna define a biome, and a sub-biome, because vegetation is more pervasive than fauna, it becomes the principal indicator in practice.

The correct answer is E. Vegetation types

Explanation:

In geography, the zones around the world are classified into five main types:  the tropical zone, the Arctic, the Antarctic, the South temperate zone, and the North temperate zone. These zones are determined by two main factors, the first one is the latitude, for example, the tropical zone is near the equator line, and the second one is the vegetation that is different in each zone. For example, the Arctic and Antarctic zones differ from others because the vegetation is not abundant and includes mainly grasses and mosses; on the opposite, in the tropical zone, the vegetation is abundant including diverse grasses, shrubs, and trees. At the same time, it is vegetation the key to determining sub-type zones. Thus, one principal indicator used to delineate the five zones is vegetation types.