Alice is involved in harvesting a natural polymer from trees, which most likely refers to natural rubber (derived from the sap of rubber trees). Julio’s job involves chemically changing that natural polymer to create a synthetic polymer, which is commonly a process that involves creating or modifying synthetic rubber (like vulcanized rubber, which is a treated form of rubber).
So, the correct answer is:
Alice works with natural rubber, and Julio works with vulcanized rubber.