"Since the 1950s, scientists have known that rapid eye movement, of REM, occurs when someone is sleeping. Previous studies attempting to determine the meaning of these eye movement have been unsuccessful in part because these studies relied on human subjects revealing the content of their dreams. A recent study by physiologist Yuta Senzai and Massimo Scanziani has avoided this issue by studying dreaming mice instead. Their results in REM is correlated to changes in direction during the dream." Which choice best describes the function of the second sentence in the overall structure of the text?A. It names a problem in the approach taken by Senzai and Scanziani.B. It introduces the difficulty that the study by Senzai and Scanziani was designed to bypass.C. It presents the findings of studies done prior to the study by Senzai and Scanziani.D. It clarifies how others studying REM sleep interpret the study by Senzai and Scanziani.

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