SAT Question 5effa190: Words In Context answer and explanation

English - Words In Context - Fill In Blank Single Word
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The process of mechanically recycling plastics is often considered ______ because of the environmental impact and the loss of material quality that often occurs. But chemist Takunda Chazovachii has helped develop a cleaner process of chemical recycling that converts superabsorbent polymers from diapers into a desirable reusable adhesive.
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Difficulty:Easy
Which choice completes the text with the most logical and precise word or phrase?