The asthenosphere is the highly viscous, mechanically weak and ductilely deforming region of the upper ______________ of Earth.

Correct option is D

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• The asthenosphere is a layer within the Earth's mantle, located beneath the lithosphere. It is a mechanically weak, ductile, and viscous region that allows for the movement of tectonic plates.
  
• The asthenosphere plays a critical role in plate tectonics by providing a semi-fluid layer over which the rigid lithosphere can move.

• The asthenosphere extends from about 100 km to 700 km beneath the Earth's surface and is composed of partially molten rock, which allows it to flow slowly over time.
• This flow facilitates the movement of tectonic plates on top of it.

• Crust and Core: The asthenosphere is not located between the crust and the core; it is part of the mantle.
• Core: The core is much deeper and is made up of the inner and outer core, not related to the asthenosphere.
• Crust: The crust is the outermost layer of the Earth, above the asthenosphere, and it is solid and rigid.