D. An X-Y coordinate system, with the origin at 0° latitude and 0° longitude
The Three Economic Sectors. According to the three-sector theory, all economic activity can be classified into one of three sectors: the primary sector, the secondary sector and thetertiary sector.
Layers of the soil are called horizons. Here are the horizons:
- Humus
- Topsoil
- Subsoil
- Fragmented rock
- Bedrock
Once a soil has developed, it forms layers called horizons. Beneath a surface layer of a plant remains, the topsoil is rich in decomposed plants and animal matter. The subsoil is mainly mineral particles, with much less organic material. The fragmented rock/bedrock is primarily small stones, and beneath it lies all bedrock.
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