D, combination of all the them
Westward expansion meant that the US acquired ever increasing amounts of land, and needed people, farmers, to settle there so it could maintained without a huge military presence
The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up into tectonic plates. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually.[2]
Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual expansion of the globe.[3]
Tectonic plates are able to move because the Earth's lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge (due to variations in topography and density of the crust, which result in differences in gravitational forces) and drag, with downward suction, at the subduction zones. Another explanation lies in the different forces generated by tidal forces of the Sun and Moon. The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate.
Answer:
D. tierra caliente, tierra templada, tierra fria, tierra helada.
Explanation:
The Latin American region has its own unique names for the elevation zones based on the climate. The lowest of them is the tierra caliente, characterized with lowlands and hills covered with dense tropical forests, and hot weather. The tierra caliente is the second, located between 1,000 and 2,000 meters, being still part of the tropical climate, but being cooler and more pleasant, which is why there are lot of big cities on this elevation. The tierra fria is located further up, up to 3,000 meters, and it is colder, dominated with grasslands, and the living conditions are not the best. The top elevation zone is the tierra helada, located in the highest parts of the Andes, being dominated by barren mountain slopes, strong winds, and cold climate.
