Which of the following factors is most necessary for an efficient respiratory surface?

Select the correct option for the shape of guard cells in stomata.

	Stomata of Monocots	Stomata of Dicots
$A$.	Bean-shaped	Dumbbell-shaped
$B$.	Dumbbell-shaped	Bean-shaped
$C$.	Bean-shaped	Bean-shaped
$D$.	Dumbbell-shaped	Dumbbell-shaped

The solubility of $CO_{2}$ in the blood is

Lungs have a large number of alveoli for....

The blood flowing towards the lungs contains more of which of the following compared to the blood flowing away from the lungs?

Given below are two statements.
Statement $I$: Respiratory membrane is composed of two layers of squamous epithelia,each resting on a thick basement membrane.
Statement $II$: The diffusion of a respiratory gas takes place from lower partial pressure to higher partial pressure of the same.
In the light of above statements,choose the most appropriate answer from the options given below: