48. Read the following sentences from the reading passage. What does “they” refer to?Scientists at Pennsylvania State University in the U.S. conducted a study in which research participantswere told that a new technology, which doesn’t actually exist, could measure their sleep quality from thenight before. They were connected to a machine monitoring brainwave frequency and shown piles ofspreadsheets and formulas. Then some were informed that their deep sleep or rapid eye movement(REM) sleep had been above average the night before, a sign they were mentally alert.
(A) scientists
(B) research participants
(C) formulas
(D) rapid eye movements