Which one is the correct structure of neoprene?

Match the following:

Column-$A$	Column-$B$
$a.$ Nylon-$6$	$I.$ Natural Rubber
$b.$ Vulcanized Rubber	$II.$ Cross Linked
$c.$ cis-$1,4$-polyisoprene	$III.$ Caprolactam
$d.$ Polychloroprene	$IV.$ Neoprene

Choose the correct answer from the options given below:

The biodegradable polymer is

Select the incorrect option for the following polymer:

Nylon $66$ is

Phenol and formaldehyde undergo condensation to give a polymer $(A)$ which on heating with formaldehyde gives a thermosetting polymer $(B)$. Name the polymers. Write the reactions involved in the formation of $(A)$. What is the structural difference between the two polymers?