The article says:
Scientists have been studying sun sneezing for a very long time. But even today, experts aren't exactly sure what causes PSR. But it might be mixed-up brain signals.
Which words from the passage help you understand the meaning of the word experts?
A.mixed-up brain signals
B.even today
C.scientists have been studying
D.a very long time
C. scientists have been studying
D. a very long time