Airborne chemical substances travel up the nose to the olfactory which is the receptor for smell.
a. bulb
b. cortex
c. cilia
d. base

Airborne chemical substances travel up the nose to the olfactory OLFACTORY CORTEX, which is the receptor for smell.

Explanation:

The olfactory cortex is the portion of the cerebral cortex that concocts olfactory data. It is required in the function of smell. It is found in the temporary lobe of the brain, which is associated with establishing sensory input. The olfactory cortex is further a part of the limbic system.

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.