PHBV (Polyhydroxybutyrate-co-hydroxyvalerate) is a biodegradable polymer. It is a type of biopolymer that is made from renewable resources and can be broken down by microorganisms in the environment, making it environmentally friendly.
Thus, the only biodegradable polymer in the options is PHBV (Option D).

Three friends, P, Q, and R, are solving a puzzle with statements:
(i) If P is a knight, Q is a knave.
(ii) If Q is a knight, R is a spy.
(iii) If R is a knight, P is a knave. Knights always tell the truth, knaves always lie, and spies sometimes tell the truth. If each friend is either a knight, knave, or spy, who is the knight?