What is the exine of a pollen grain made of?

What is the approximate diameter of a pollen grain?

Because of which substance are pollen grains well preserved as fossils?

Which substance provides protection to pollen grains against high temperatures?

Given below are two statements.
Statement $I$: Generally,anthers in angiosperms are dithecous,having two pollen sacs in each lobe.
Statement $II$: Each sporangium produces pollens from sporogenous tissues by the process of sporogenesis.
In light of the above statements,select the correct answer from the options given below.

Which of the following statements is correct?