Generally,how many middle layers are formed in the wall of the anther lobes?

In over $60\%$ of angiosperms,pollen grains are shed at which of the following stages?

The pollen grain is

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:

Isobilateral tetrads are commonly found in........

What is the typical diameter of a pollen grain?