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Question 149·Hard·Words in Context

Microbiologists found that an enzyme-producing bacterial strain received little protection from its enzyme because the molecule diffused away, while a capsule-bearing strain produced no enzyme and was also vulnerable. In mixed colonies, however, the capsule trapped the enzyme near both strains, sharply improving their survival. Because this protection appeared only through interaction and was not present in either strain alone, researchers described it as an ______ property of the mixed colony.

Which choice completes the text with the most logical and precise word or phrase?