In angiosperms,all $4$ microspores of a tetrad are covered by a layer which is formed by:

The saccus of $Pinus$ pollen is a modification of:

$A$: Each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad.
$R$: The most abundant type of microspore tetrad is the product of simultaneous cytokinesis.

$A$ typical angiosperm anther is:

$A$ - Due to meiosis in $MMC$,microspore tetrads are produced.
$R$ - $MMC$ is a large cell containing dense cytoplasm and a prominent nucleus.

$A$ microspore mother cell forms