The forward section of the nasal cavity within and above each nostril is called as a vestibule. This region of the nose is lined by stratified squamous epithelium on which stiff hairs are present which prohibit entry of dust particles coming along with the inspired air. 

Nose is a most important sense organ of smell. The human nose can detect approximately 10,000 different odours. Nose also helps in the process of respiration.

Above the uppermost concha, is the olfactory bulb. It processes information about odours.
The entire nasal cavity is lined by a moist mucous membrane supplied with a large number of blood vessels.
The mucous membrane also has fine hair-like projections called the cilia which collect any debris entering the nasal cavity.
Apart from the cilia, the mucous membrane also has several cells. Some of these cells are called as secretory cells. Secretory cells secrete a thick, viscous fluid called as the mucous.

Flavour is a combination of taste and smell while eating or sipping. There are two types of receptors like gustato receptors and olfactory receptors which are involved in the sense of taste and smell respectively.

The receptors for smell are located in the olfactory epithelium in the nose or nasal chamber thus, whatever comes near to our nose we can immediately sense its smell.

Bowman's glands are branched tubular glands in the olfactory mucous membrane. The structure of the Bowman's glands consists of an acinus in the lamina propria and a secretory duct going out through the olfactory epithelium. Bowman's glands secrete proteins, such as lysozyme, amylase and IgA similar to serous glands. 

•  Humans possess a tiny, shiny crystal of magnetite in the ethmoid bone, located between your eyes, just behind the nose.
•  Magnetite is a magnetic mineral also possessed by homing pigeons, migratory salmon, dolphins, honeybees, and bats is a tiny compass needle, allowing them to orient themselves in the earth's magnetic field and swim down to their happy home in the mud. Hence, Some persons have an innate sense of direction. It is due to the magnetic sensitivity of the Nose.

 Both olfactory receptors and sound receptors have cilia. The different senses are taste, smell, vision and auditory senses. In humans, specialized sensory receptors are present in distinct sense organs that detect the sensory stimuli and transmit the stimuli as nerve impulses to the brain.

The following are disorders of olfaction: Anosmia inability to smell. ysosmia things smell different from memory or expectation. Hyperosmia an abnormally acute sense of smell. Hyposmia decreased ability to smell.

Fact:
On increasing age,olfactory sensation decreases. In female humans, the sense of olfaction is strongest around the time of ovulation, significantly stronger than during other phases of the menstrual cycle and stronger than the sense in males.

(A)Audition is the sense of hearing.

Olfactory receptors are found in nose. They are associated with the perception of smell. Olfactory receptors expressed in the cell membranes of olfactory receptor neurons are responsible for the detection of odor molecules. Activated olfactory receptors are the initial player in a signal transduction cascade which ultimately produces a nerve impulse which is transmitted to the brain.

• Olfactory receptors are also known as odorant receptors. 
• They are present in the cell membranes of olfactory receptor neurons and are responsible for the detection of odour which gives rise to the sense of smell.
• Hence,  Olfactory receptor organs are sensitive to Smell.
• So, the correct answer is 'Smell'.