When microspores are formed, they exist as a cluster of how many cells?

Identify $A$ to $F$ in the following diagram.

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:

Which are the three cells found in a pollen grain when it is shed at the three-celled stage?

Which part of the reproductive structure produces both enzymes and hormones?

What is the exine of a pollen grain made of?