A: Are you feeling well, Sally? 76____________________
B: I watched a good TV play last night. I didn' t go to bed until midnight.
A: 77____________________
B : Yes, I do. And I seldom go to bed before eleven because of watching TV.
A: Then you don' t have enough sleep. You can' t work well at class the next day. What' s more, it' s bad for your health. 78____________________
B: I sleep for about seven hours a night. How many hours' sleep is enough then?
A: As teenagers, we should sleep at least eight hours a day.
B: 79____________________I' 11 go to bed before nine o' clock and get up at seven o'clock from now on.. Good -bye!
A: 80____________________
第76空正确答案是（　　）