The number of pollen sacs in a dithecous anther is

Given below are two statements: One is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$
Assertion $(A) :$ Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus.
Reason $(R):$ Presence of more than one nucleus in the tapetum increases the efficiency of nourishing the developing microspore mother cells.
In light of the above statements,choose the most appropriate answer from the options given below:

Microsporogenesis is:

The generative cell of a two-celled pollen divides in the pollen tube but not in a three-celled pollen. Give reasons.

Identify the labelled part $X$ from the figure:

In over $60\%$ of angiosperms,pollen grains are shed at the $2$-celled stage. In less than $40\%$ of angiosperms,pollen grains are shed at the $3$-celled stage.