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Question 138·Hard·Transitions

Archaeologists recently examined residues on ancient Scandinavian pottery and identified traces of birch bark tar, a substance known to have been used as an adhesive for stone tools. Their analysis showed that the tar was often mixed with beeswax, a combination that enhances pliability and strength. ______ isotopic tests on residues from neighboring sites revealed a different recipe: pine resin blended with animal fat.

Which choice completes the text with the most logical transition?