Read the following four statement carefully.
(i) Ventral respiratory group of neurons of medulla oblongata can cause both inspiration and expiration.
(ii) The part of the respiratory system starting with the external nostrils up to the terminal bronchioles constitutes the respiratory or exchange part of the respiratory system.
(iii) During swallowing epiglottis can be covered by a thin elastic cartilaginous flap called glottis to prevent the entry of food into the larynx.
(iv) Binding of oxygen with haemoglobin in primarily related of oxygen with haemoglobin is primarily related to partial prssure of `O_(2)`.
Which of the above two statement are correct ?

Options

A. a) `(ii)` and `(iii)`
B. b) `(iii)` and `(iv)`
C. c) `(i)` and `(ii)`
D. d) `(i)` and `(iv)`

Explanation

To determine which of the four statements are correct, we will analyze each statement one by one.

### Step 1: Analyze Statement (i)
**Statement:** Ventral respiratory group of neurons of medulla oblongata can cause both inspiration and expiration.

**Analysis:** This statement is correct. The ventral respiratory group (VRG) in the medulla oblongata is responsible for generating the rhythm of breathing and can initiate both the inhalation (inspiration) and exhalation (expiration) processes.

### Step 2: Analyze Statement (ii)
**Statement:** The part of the respiratory system starting with the external nostrils up to the terminal bronchioles constitutes the respiratory or exchange part of the respiratory system.

**Analysis:** This statement is incorrect. The part of the respiratory system that includes the external nostrils up to the terminal bronchioles is known as the conducting zone, which is responsible for conducting air to the lungs. The respiratory or exchange part of the respiratory system is primarily the alveoli, where gas exchange occurs.

### Step 3: Analyze Statement (iii)
**Statement:** During swallowing, the epiglottis can be covered by a thin elastic cartilaginous flap called glottis to prevent the entry of food into the larynx.

**Analysis:** This statement is incorrect. The epiglottis is the flap that covers the glottis (the opening to the larynx) during swallowing to prevent food from entering the airway. The glottis itself is not a flap; it is the space between the vocal cords.

### Step 4: Analyze Statement (iv)
**Statement:** Binding of oxygen with hemoglobin is primarily related to the partial pressure of O2.

**Analysis:** This statement is correct. The binding of oxygen to hemoglobin is indeed influenced by the partial pressure of oxygen. Higher partial pressures of oxygen facilitate the binding of oxygen to hemoglobin.

### Conclusion
Based on the analysis:
- **Correct Statements:** (i) and (iv)
- **Incorrect Statements:** (ii) and (iii)

### Final Answer
The two correct statements are **(i) and (iv)**.