Which process are the guard cells associated with?

Which of the following facilitates opening of stomatal aperture?

Given below is the diagram of a stomatal apparatus. In which of the following are all the four parts labelled as $A, B, C$ and $D$ correctly identified?

When the relative humidity of the atmosphere is $100\%$ during the daytime,the stomata shall:

Which of the following is $NOT$ included in the stomatal apparatus?

Arrange the events of opening stomata in correct sequence and choose the correct option accordingly.
$I.$ Lowering of osmotic potential of guard cells
$II.$ Decline in guard cell solute
$III.$ Rise of potassium ion level in guard cells
$IV.$ Guard cells absorb water from neighbouring epidermal cells
$V.$ Guard cells become flaccid
$VI.$ Guard cells swell and create a pore between them