Which of the following best describes the compositional layers of the earth?
a. all layers of the earth below the crust are liquid.
b. the only liquid layer of the earth is the mantle.
c. the crust floats on top of the outer core.
d. some layers of the earth are liquid, and some are solid.

The answer to the question is letter D. Some layers of the earth are liquid, and some are solid.

>The Earth is made up of three layers: crust;mantle;and, core.
> Crust: are composed of dense iron magnesium silicate igneous rocks, like basalt. The crust is solid.
> Mantle:composed of silicate rocks, rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause the silicate material to be sufficiently ductile. 
> Core:(outer core) composed primarily of iron and some nickel; not necessarily a solid, but, because it is able to deflect seismic waves, it must behave as a solid in some way;(inner core) inner core will depend on whether the inner core is a solid or is a plasma with the density of a solid.

Neurotransmitters are messengers responsible for communication between neurons. they are released from synaptic vesicles and are received by receptors.  the communication is referred to as neurotransmission. the following statement is true about neurotransmitters: a. they're stored in synaptic vesicles in the axon.