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Based on the context of the passage, what is a synonym for the words in bold?

Eco-Friendly Surfing

Neoprene, a synthetic(bold) a) established b) proven c) recognized d) artificial rubber developed by physicist Hugh Bradner in a University of California, Berkeley laboratory, has been used to make wetsuits since the 1950s. The rubber emits a relatively high amount of carbon gases, which in large quantity and over a prolonged period, have been shown to be harmful to the environment. One wetsuit manufacturer has introduced a wetsuit made from the tropical hevea tree. Unlike neoprene, which is made from nonrenewable(bold) a) limited b) controlled c) predictable d) predetermined resources, hevea is a sustainable, non-toxic resource for many products, including a stretchy rubber that is perfect for wetsuits. With these wetsuits, surfers can be confident that they are not only enjoying the environment, but helping to protect it as well.