Case: Read the passage and answer the following questions

A large number of polymers are quite resistant to the environmental degradation processes and are thus responsible for the accumulation of polymeric solid waste materials. These solid wastes cause acute environmental problems and remain undegraded for quite a long time. In view of the general awareness and concern for the problems created by the polymeric solid wastes, certain new biodegradable synthetic polymers have been designed and developed. These polymers contain functional groups similar to the functional groups present in bio-polymers. Aliphatic polyesters are one of the important classes of biodegradable polymers.

What are the monomeric units of PHBV?

3-Hydroxybutyric acid + 3-Hydroxyvaleric acid