(3) Most of us go to bed at night and wake up in the morning.  44  , when it comes toanimals, sleep duration varies widely among animal classes and species. For instance, youmay know brown bears hibernate and goldfish sleep with their eyes open. But why do theirsleep habits  45  in animal kingdom? That is because they have to worry about  46  someone will try to eat them while they’re snoozing!   The following are amazing facts about animal sleeping habits. Dolphins havesomething called unihemispheric sleep. It means one side of the brain sleeps while the other is  47  . When this takes place, they are able to keep one eye  48  to keep a look out for anypredators. The second fun fact is about giraffes. Since they are difficult to  49  or get upquickly, sleeping is a huge trouble for them; therefore, as giraffes sleep, they usually have just30 minutes per day. As to sea otters, they often float on their backs and hold hands whilesleeping. The reason why sea otters hold hands while sleeping is so that they don’t drift away  50  each other when they are in deep sleep. It is quite mysterious about sleep, right?
【題組】44
(A) However
(B) Moreover
(C) Thus
(D) Afterward