$$ \text { The structure given below is an example of } $$

I. A condensation and biodegradable polymer.

II. A biodegradable and thermoplastic polymer.

III. A biodegradable and thermosetting polymer.

IV. A polyester and thermoplastic polymer.

Which one among the following is a semi-synthetic polymer?

$$ \text { Monomeric units of melamine polymer are } $$

Type of reaction involved in the initial step in the formation of bakelite