Final answer:
The material in the asthenosphere is solid rock that behaves in a plastic manner due to the conditions within the Earth. It is composed of mantle rock and is not magma, lava, or core material.
Step-by-step explanation:
The asthenosphere is a region in the Earth's mantle characterized by its semi-fluid properties that allow it to flow slowly. Despite sometimes being mistaken for a liquid, the material in the asthenosphere is actually solid rock that behaves plastically due to high temperature and pressure conditions. This region is composed of mantle rock, which is an ultramafic composition containing more iron and magnesium compared to the crust. The asthenosphere plays a crucial role in the movement of tectonic plates on the Earth's surface.
When material from the upper mantle is ejected from volcanoes, it is called magma when it is below the Earth's surface and referred to as lava after it erupts. However, neither magma nor lava is correct in this context as they relate to volcanic activity. The core of the Earth consists of a liquid outer core and a solid inner core, made primarily of iron and nickel. These layers are more dense and are composed of different material than the mantle.
Therefore, the correct answer for the substance in the asthenosphere would be mantle, not magma, lava, or core.