Identify $A$ and $B$ in the diagram given below:

Anther is generally composed of

Choose the correct option regarding the anther.

When a pollen grain is shed at the $3$-celled stage,name the cells it contains.

$P -$ This cell is big,has abundant food reserve and a large irregularly shaped nucleus.
$Q -$ This cell is small and floats in the cytoplasm of the vegetative cell. It is a spindle-shaped cell with dense cytoplasm and a nucleus.
$\quad\quad \quad P \quad \quad Q$

Arrange the following in the correct developmental sequence related to microsporogenesis:
$A$. Microspore tetrads
$B$. Sporogenous tissue
$C$. Pollen grains
$D$. Pollen mother cells
Choose the correct answer from the options given below: