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Question 93·Hard·Transitions

Lingering just beyond the edges of Saturn’s bright rings is an elusive structure known as the Phoebe ring. Astronomers long suspected its existence because of unexplained dust patterns around the planet. ______ a recent survey using NASA’s infrared telescope confirmed that the ring extends millions of miles into space, dwarfing Saturn’s better-known neighbors.

Which choice completes the text with the most logical transition?